Systems and methods for humidity determination and uses thereof

ABSTRACT

Methods and systems are provided for conducting measurements of relative humidity via the use of an ultrasonic sensor. In one example, the ultrasonic sensor for conducting the relative humidity measurement is selected from a plurality of ultrasonic sensors positioned at various locations on the vehicle, and where the selecting is accomplished in some examples via the use of one or more onboard cameras configured to identify suitable objects that are stationary with respect to the vehicle. In this way, robustness and accuracy of relative humidity measurements may be improved, lifetime of individual ultrasonic sensors may be extended, and vehicle operating conditions that depend on accurate relative humidity measurements may be improved.

FIELD

The present description relates generally to methods and systems fordetermining relative humidity via ultrasonic sensors or other means, andbased on the humidity determination, adjusting one or more vehicleoperating parameters.

BACKGROUND/SUMMARY

One or more ultrasonic sensors may be mounted on an automotive vehicle,for example a hybrid electric vehicle (HEV), enabling a distancedetermination between the sensor and an external object. Such anultrasonic sensor may consist of at least a piezoelectric disc and amembrane, configured to convert electrical energy into mechanicalenergy, and mechanical energy into electrical energy. More specifically,an oscillated voltage may be applied to the piezo disc such that thepiezo disc and membrane vibrate and generate ultrasonic waves at afrequency based on the frequency of voltage oscillation. After the wavesare emitted, sensors wait for echoes to come back from objects, and whenthe echoes interact with the sensor/membrane, the membrane is excited tovibrate. The piezo disc attached to the membrane converts the vibrationto voltage, and based on the timeframe of sending and receiving theultrasonic wave, a distance determination to an object may be inferred.

In a vehicle, ultrasonic sensors may be utilized for inferring distancebetween a vehicle and obstacles during either assisted, or fullyautomated parking, for example. However, there are a number of factorsthat may affect optimal operation of an ultrasonic sensor. Such factorsmay include temperature, humidity, target surface angle, and reflectivesurface roughness. Of these four variables, determining humidity in avehicle may be complicated, particularly in a case where a vehicle maynot include a dedicated humidity sensor.

US Patent Application US 20060196272 teaches the use of an ultrasonicsensor configured to transmit two different frequencies, and estimatehumidity based on a difference between attenuation losses obtained fromthe two different frequencies. However, the inventors herein haverecognized potential issues with such systems. As one example, US20060196272 does not teach methods for selecting which ultrasonic sensorto use for conducting a relative humidity measurement, in a conditionwhere a plurality of ultrasonic sensors are positioned on the vehicle.

Furthermore, in some examples, ultrasonic sensors may be utilized todetect an object that is close to a rear of a vehicle, for instanceprior to a diesel particulate filter (DPF) regeneration procedure in avehicle powered by diesel fuel. More specifically, US Patent ApplicationUS 2012/0023910 teaches controlling regeneration of a DPF based onwhether an object is detected within a threshold distances of thevehicle exhaust. However, the inventors have additionally recognizedpotential issues with such a system. For example, US 2012/0023910 doesnot teach the potential for adjusting distance thresholds in order tocontrol DPF regeneration events.

Thus, the inventors herein have developed systems and methods to atleast partially address the above issues. In one example, a method isprovided, comprising selecting one of a plurality of sensors positionedaround a motor vehicle; transmitting a plurality of signals from theselected sensor, each at a different frequency; receiving reflectedsignals of the transmitted signals; determining attenuation values onlyfor each of the reflected signals which have the same transit time fromtransmission to receipt; determining differences between pairs of theattenuation values; and converting the differences to an indication ofrelative humidity.

As one example, the method includes regenerating a particulate filtercoupled to an underbody of the motor vehicle by causing burning ofparticulate stored in the particulate filter resulting in hot gasesexiting a rear of the motor vehicle; selecting the selected sensor basedon a transmission path of the selected sensor overlapping at least aportion of the hot gases exiting the rear of the motor vehicle; andpostponing or aborting the regeneration based on there being an objectwithin a predetermined distance of the hot gases exiting the rear of themotor vehicle. In an example, the method may further include measuringan air temperature near where the hot gases exit the rear of the motorvehicle; determining thermal conductivity of air based, at least inpart, on the indication of relative humidity and the air temperature;and adjusting a distance threshold for the regeneration procedure, wherethe adjusting the distance threshold includes decreasing the distancethreshold as thermal conductivity decreases, and increasing the distancethreshold as thermal conductivity increases. In this way, a suitablesensor may be selected from a plurality of ultrasonic sensors fordetermining relative humidity, such that a measurement of relativehumidity may be determined. Furthermore, responsive to the indication ofrelative humidity, the relative humidity measurement may be utilized toadjust a distance threshold for DPF regeneration, which may thus resultin greater completion frequency for DPF regeneration events.

The above advantages and other advantages, and features of the presentdescription will be readily apparent from the following DetailedDescription when taken alone or in connection with the accompanyingdrawings.

It should be understood that the summary above is provided to introducein simplified form a selection of concepts that are further described inthe detailed description. It is not meant to identify key or essentialfeatures of the claimed subject matter, the scope of which is defineduniquely by the claims that follow the detailed description.Furthermore, the claimed subject matter is not limited toimplementations that solve any disadvantages noted above or in any partof this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic depiction of an internal combustion engine.

FIG. 2 shows a block diagram of components of a vehicle system that usesultrasonic sensor(s) for assisting or controlling vehicle parkingmaneuvers.

FIG. 3A depicts a graph detailing effects of humidity and ultrasonicfrequency on sound attenuation.

FIG. 3B depicts a graph illustrating a difference in sound attenuationfor different ultrasonic frequencies, at a particular relative humidity.

FIG. 3C graphically depicts an example transfer function for determiningrelative humidity as a function of a difference in sound attenuation fortwo ultrasonic frequencies.

FIG. 4 shows a high level example method for conducting a relativehumidity determination via the use of an ultrasonic sensor.

FIG. 5 shows a high level example method for conducting a variablefrequency algorithm used by an ultrasonic sensor, as a sub-method ofFIG. 4.

FIG. 6 shows a high level example method for conducting a deltaattenuation calculation, as a sub-method of FIG. 4.

FIG. 7 shows a high level example method for using one or more onboardcamera(s) for selecting an appropriate ultrasonic sensor for conductinga relative humidity measurement.

FIG. 8 shows a schematic diagram of an example UEGO sensor.

FIG. 9 shows a high level example method for opportunisticallyconducting a humidity measurement using either an oxygen sensor or anultrasonic sensor, responsive to environmental or vehicle operatingconditions.

FIG. 10 depicts a graph illustrating thermal conductivity of air as afunction of ambient temperature and humidity.

FIG. 11 shows a high level example method for conducting a dieselparticulate filter regeneration procedure, based on whether an object isdetected positioned in an area close to a vehicle exhaust.

FIG. 12 shows a high level example method for adjusting a distancedetection threshold for an ultrasonic sensor.

FIG. 13 depicts an example lookup table that may be used in conjunctionwith the method of FIG. 12, for selecting optimal ultrasonicfrequency(s) for distance measurements, based on adjusted distancedetection thresholds.

FIG. 14 shows an example timeline for conducting a humiditydetermination procedure based on vehicle operating conditions.

FIG. 15 shows an example timeline for conducting a DPF regenerationevent, where conditions of the regeneration event may be at leastpartially based on an indication of ambient humidity.

DETAILED DESCRIPTION

The following description relates to systems and methods for conductingrelative humidity measurements and adjusting vehicle operationparameters responsive to the relative humidity determination. Suchmeasurements may be carried out by a vehicle system including aninternal combustion engine, where the vehicle may further be configuredwith one or more onboard camera(s) and one or more ultrasonic sensor(s),such as the vehicle system depicted in FIG. 1. In some examples, thevehicle may be a hybrid vehicle that can operate for extended timeperiods without operation of the engine. Knowledge of relative humiditymay improve functions such as assisted or fully-automated parkingprocedures, where the procedures may be enabled via a parking assistsystem as illustrated in FIG. 2. In some examples, humidity measurementsmay be determined via an ultrasonic sensor, based on a relationshipbetween sound attenuation, relative humidity, and ultrasonic frequency,as illustrated in FIG. 3A. For example, a difference in soundattenuation for a given pair of frequencies may enable an estimation ofambient humidity, indicated by FIG. 3B. Such an estimation may beconducted via a transfer function, graphically depicted in FIG. 3C.

FIG. 4 illustrates a high level example method for conducting a humiditymeasurement via the use of an ultrasonic sensor. As a sub-method of FIG.4, a variable frequency algorithm as depicted in FIG. 5 may be used todetermine sound attenuation for two or more ultrasonic frequency(s),which may then enable a delta attenuation calculation, as depicted inFIG. 6. By conducting the variable frequency algorithm and the deltaattenuation calculation, a relative humidity measurement may bedetermined.

In some examples, one or more onboard camera(s) may be utilized toidentify suitable objects of interest for conducting the humiditydetermination procedure via the use of an ultrasonic sensor.Accordingly, a method for detecting suitable objects via the use of oneor more camera(s) is illustrated in FIG. 7.

In further examples, some conditions may not be optimal for enabling ahumidity determination via an ultrasonic sensor, and another means maybe desirable, and vice versa. For example, an oxygen sensor positionedin an intake or exhaust manifold of a vehicle engine may be used in lieuof an ultrasonic sensor to indicate humidity under particular vehicleoperation conditions. Such an example of an oxygen sensor is illustratedin FIG. 8, and an example method for selecting whether to conduct ahumidity measurement via an oxygen sensor or an ultrasonic sensor, basedon vehicle operating conditions, is illustrated in FIG. 9.

The vehicle system depicted in FIG. 1 may in some examples comprise adiesel engine, and may thus include a diesel particulate filter (DPF)for capturing and storing soot from the engine. Regeneration of such afilter may include high exhaust temperatures, and thus it may bedesirable in some examples to indicate whether an object is within aproximity of the exhaust prior to conducting the regeneration procedure.Furthermore, distance thresholds for the object may in some examples beadjusted as a function of relative humidity and temperature in alocation near the exhaust. For example, thermal conductivity of air mayvary as a function of humidity and temperature, indicated by the graphdepicted in FIG. 10. Accordingly, a distance threshold for an object mayin some examples be adjusted, based on an inferred thermal conductivityof air, as illustrated in the method depicted in FIG. 11. By adjusting adistance threshold, DPF regeneration procedures may be enable to executemore frequently, for example.

As discussed above, humidity may comprise a noise factor for operationaluse of an ultrasonic sensor. Thus, in some examples, knowledge ofambient humidity may improve operational use of the ultrasonic sensor.In one example, a distance detection threshold may be adjusted,according to the method illustrated in FIG. 12. As an example, adjustingthe distance detection threshold may include indicating suitablefrequencies for conducting a distance measurement using an ultrasonicsensor. In such an example, a lookup table, such as the lookup tableillustrated in FIG. 13 may be used in conjunction with the methodillustrated in FIG. 12, in order to determine an optimal frequency for adesired operational use of the ultrasonic sensor.

Example timelines for selecting humidity determination methodology basedon vehicle operating procedures, and for conducting a DPF regenerationprocedure based at least in part on a humidity determination, areillustrated in FIG. 14, and FIG. 15, respectively.

FIG. 1 is a schematic diagram showing one cylinder of a multi-cylinderengine 10 in an engine system 100. The engine system 100, may be coupledinside a propulsion system of an on road vehicle system 101. An outsideair temperature (OAT) sensor 127 may be positioned on the exterior ofthe vehicle system 101. The OAT sensor may estimate the ambient airtemperature that may be used for engine operations and in addition, OATsensor 127 may be used in some examples to trigger humidity measurementscorresponding to a change in ambient temperature. In some examples, oneor more camera(s) 186 may be positioned at one or more positions (e.g.locations) on the vehicle, and may be configured to obtain imagesincluding, but not limited to, an environment around the vehicle. Insome examples, one or more camera sensor(s) (e.g. 187) may be configuredto provide positional information regarding the one or more camera(s)186. For example, if a camera is rotatable, camera sensor(s) 187 mayconvey a direction that the camera is facing to a vehicle controller(e.g. 12). In other examples, where the camera is not rotatable, camerasensor(s) 187 may still be configured to indicate position and adirection the camera is facing. Furthermore, one or more ultrasonicsensor(s) 185 may be positioned at one or more positions on the vehicle,and may be configured to measure distance from the ultrasonic sensor(s)and an object of interest. For example, the ultrasonic sensor may beconfigured to transmit and receive signals in the form of sound waves.In some examples, an object of interest may be detected by theultrasonic sensor(s) themselves. In other examples, the one or morecamera(s) may detect an object of interest, whereupon the ultrasonicsensor(s) may be utilized to conduct a distance measurement between theultrasonic sensor(s) and the object of interest. In still furtherexamples, as will be discussed in detail further below, the ultrasonicsensor(s) may be utilized to obtain relative humidity measurements. Forexample, certain conditions may trigger a request for a relativehumidity measurement, where the certain conditions may include a changein temperature greater than a predetermined temperature threshold, anambient pressure change greater than an ambient pressure threshold, athreshold of time of engine operation or distance of vehicle travelgreater than a threshold distance since a previous (e.g. last) humiditymeasurement.

More specifically, as will be described further below, in some examplesultrasonic sensor 185 may be utilized to obtain distance proximitymeasurements between a vehicle and object(s) of interest (e.g.obstacles) during a vehicle operation such as an assisted orfully-automated parking maneuver. However, a noise factor for theultrasonic sensor(s) 185 may be humidity. Thus, in some examples,knowledge of relative humidity may be used to adjust a detectionthreshold of the ultrasonic sensor, which may involve indicatingsuitable frequencies for conducting distance measurements using theultrasonic sensor. In still further examples, knowledge of relativehumidity may improve engine operating conditions where such conditionsrely on an accurate estimation of relative humidity, as will bediscussed further below.

Engine 10 may be controlled at least partially by a control systemincluding controller 12 and by input from a vehicle operator 132 via aninput device 130. In this example, input device 130 includes anaccelerator pedal and a pedal position sensor 134 for generating aproportional pedal position signal PP. Combustion chamber (i.e.,cylinder) 30 of engine 10 may include combustion chamber walls 32 withpiston 36 positioned therein. Piston 36 may be coupled to crankshaft 40so that reciprocating motion of the piston is translated into rotationalmotion of the crankshaft. Crankshaft 40 may be coupled to at least onedrive wheel of a vehicle via an intermediate transmission system.Further, a starter motor may be coupled to crankshaft 40 via a flywheelto enable a starting operation of engine 10.

Combustion chamber 30 may receive intake air from intake manifold 44 viaintake passage 42 and may exhaust combustion gases via exhaust passage48. Intake manifold 44 and exhaust passage 48 can selectivelycommunicate with combustion chamber 30 via respective intake valve 52and exhaust valve 54. In some embodiments, combustion chamber 30 mayinclude two or more intake valves and/or two or more exhaust valves.

In this example, intake valve 52 and exhaust valves 54 may be controlledby cam actuation via respective cam actuation systems 51 and 53. Camactuation systems 51 and 53 may each include fixed cam timing, or mayinclude one or more cams and may utilize one or more of cam profileswitching (CPS), variable cam timing (VCT), variable valve timing (VVT)and/or variable valve lift (VVL) systems that may be operated bycontroller 12 to vary valve operation. The position of intake valve 52and exhaust valve 54 may be determined by position sensors 55 and 57,respectively. In alternative embodiments, intake valve 52 and/or exhaustvalve 54 may be controlled by electric valve actuation. For example,cylinder 30 may alternatively include an intake valve controlled viaelectric valve actuation and an exhaust valve controlled via camactuation including CPS and/or VCT systems.

Fuel injector 66 is shown coupled directly to combustion chamber 30 forinjecting fuel. In this manner, fuel injector 66 provides what is knownas direct injection of fuel into combustion chamber 30. The fuelinjector may be mounted in the side of the combustion chamber or in thetop of the combustion chamber, for example. Fuel may be delivered tofuel injector 66 by a fuel system (not shown) including a fuel tank, afuel pump, and a fuel rail, which may be a common fuel rail.

Intake manifold 44 may include a throttle 62 having a throttle plate 64.However, in other examples, the throttle may be located in intakepassage 42. In this particular example, the position of throttle plate64 may be varied by controller 12 via a signal provided to an electricmotor or actuator included with throttle 62, a configuration that iscommonly referred to as electronic throttle control (ETC). In thismanner, throttle 62 may be operated to vary the intake air and/or EGRprovided to combustion chamber 30 among other engine cylinders. Theposition of throttle plate 64 may be provided to controller 12 bythrottle position signal TP. Intake passage 42 may include a mass airflow sensor 120 and a manifold air pressure sensor 122 for providingrespective signals MAF and MAP to controller 12.

In some examples, engine 10 may further include a compression devicesuch as a turbocharger or supercharger including at least a compressor162 arranged along intake manifold 44. For a turbocharger, compressor162 may be at least partially driven by a turbine 164 (e.g., via ashaft) arranged along exhaust passage 48. For a supercharger, compressor162 may be at least partially driven by the engine and/or an electricmachine, and may not include a turbine. Thus, the amount of compression(e.g., boost) provided to one or more cylinders of the engine via aturbocharger or supercharger may be varied by controller 12. Further, asensor 123 may be disposed in intake manifold 44 for providing a BOOSTsignal to controller 12.

Engine 10 may further include a high pressure EGR system 150. Highpressure EGR system 150 may include an EGR conduit 152 coupled to theexhaust 48 upstream of turbine 164 and coupled to the intake 44downstream of compressor 162. High pressure EGR system 150 may includean EGR valve 154 disposed along EGR conduit 152 to control exhaust flowthrough EGR system 150. Engine 10 may also include a low pressure EGRsystem 156. Low pressure EGR system 156 includes an EGR conduit 158coupled to the exhaust 48 downstream of turbine 164 and coupled to theintake 44 upstream of compressor 162. Low pressure EGR system 156 mayinclude an EGR valve 160 disposed along EGR conduit 152 to controlexhaust flow through EGR system 156.

Controller 12 is shown in FIG. 1 as a microcomputer, includingmicroprocessor unit 102, input/output ports 104, an electronic storagemedium for executable programs and calibration values shown as read onlymemory chip 106 in this particular example, random access memory 108,keep alive memory 110, and a data bus. Controller 12 may receive varioussignals from sensors coupled to engine 10, in addition to those signalspreviously discussed, including measurement of inducted mass air flow(MAF) from mass air flow sensor 120; engine coolant temperature (ECT)from temperature sensor 112 coupled to cooling sleeve 114; a profileignition pickup signal (PIP) from Hall effect sensor 118 (or other type)coupled to crankshaft 40; throttle position (TP) from a throttleposition sensor; and absolute manifold pressure signal, MAP, from sensor122. Engine speed signal, RPM, may be generated by controller 12 fromsignal PIP. Manifold pressure signal MAP from a manifold pressure sensormay be used to provide an indication of vacuum, or pressure, in theintake manifold. Further sensors may include camera sensors 187,ultrasonic sensors 185, OAT sensor 127, etc.

Storage medium read-only memory 106 can be programmed with computerreadable data representing instructions executable by processor 102 forperforming the methods and control strategies described below as well asother variants that are anticipated but not specifically listed.

In addition, controller 12 may receive data from an onboard navigationsystem 34 (e.g. a Global Positioning System (GPS)) that an operator ofthe vehicle may interact with. The navigation system 34 may include oneor more location sensors for assisting in estimating vehicle speed,vehicle altitude, vehicle position/location, etc. This information maybe used to infer engine operating parameters, such as local barometricpressure, for example. Controller 12 may further be configured toreceive information via the internet or other communication networks 13.In some examples, information received from the GPS may becross-referenced to information available via the internet to determinelocal weather conditions, etc. Controller 12 may in some examples usethe internet to obtain updated software modules which may be stored innon-transitory memory.

As described above, FIG. 1 shows only one cylinder of a multi-cylinderengine; however it should be appreciated that each cylinder maysimilarly include its own set of intake/exhaust valves, fuel injector,spark plug, etc.

In some examples the engine may be a diesel engine configured to combustdiesel fuel (e.g. petroleum diesel or bio-diesel) via compressionignition. However, in other examples, the engine may not comprise adiesel engine. For brevity, FIG. 1 illustrates an engine where some ofthe components are included in a diesel engine, and where the rest ofthe components may be included in either a diesel engine or a non-dieselengine. As such, components specific to a diesel engine will be pointedout as being specific to a diesel engine, in the remaining descriptionof FIG. 1.

Exhaust gas sensor 126 is shown coupled to exhaust passage 48 upstreamof emission control device 70. Sensor 126 may be any suitable sensor forproviding an indication of exhaust gas air/fuel ratio such as a linearoxygen sensor or UEGO (universal or wide-range exhaust gas oxygen), atwo-state oxygen sensor or EGO, a HEGO (heated EGO), a NO_(x), HC, or COsensor. A detailed embodiment of a UEGO sensor is described withreference to FIG. 8. This sensor may be used for ambient humidityestimation under selected vehicle operating conditions. In someexamples, the engine system may include dedicated ambient humiditysensors for measurement of ambient humidity when a humidity estimationis triggered. A change in ambient temperature as measured or estimatedfrom OAT 127 and/or IAT sensor 125 may be used as a trigger for humiditymeasurement. Similarly, a change in ambient pressure as estimated by theBP sensor 128 may trigger a humidity measurement. If a differencebetween the current ambient temperature or pressure and the ambienttemperature or pressure at the last known humidity measurement is higherthan a threshold, a humidity measurement may be triggered. The humiditysensors may be positioned at the intake passage 42 and/or at the exhaustpassage 48 upstream of an emission control device 70. By activelysensing humidity during ambient conditions when humidity is expected tochange, rather than (or in addition to) opportunistically sensinghumidity when possible, a more accurate and reliable humidity estimatemay be provided for engine control and also unnecessary humiditymeasurements may be avoided.

In some examples, a humidity estimate may be conducted via either theultrasonic sensors, or via another means, such as UEGO sensor 126. Sucha method may include indicating relative humidity from differencesbetween pairs of reflected signals from a single ultrasonic sensorcoupled to a vehicle, each of the reflected signals having substantiallyequivalent transit time from an object back to the ultrasonic sensor;indicating relative humidity from one or more sensors coupled to thevehicle other than the ultrasonic sensor (e.g. UEGO sensor); andselecting which relative humidity indication method to use in responseto environmental or vehicle operating conditions. As such, humidityestimations may be timely and accurately inferred, which may improvevehicle operating conditions where such operating conditions rely onaccurate humidity estimations.

Emission control device 70 is shown arranged along exhaust passage 48downstream of exhaust gas sensor 126. Device 70 may include one or moreof at least a three-way catalyst, lean NOx trap, diesel oxidationcatalyst (DOC), selective catalytic reduction (SCR) catalyst, oxidationcatalyst, etc. An ammonia (or urea) delivery system may be coupled tothe SCR catalyst or upstream of the SCR catalyst to deliver reductant tothe SCR catalyst.

In an example where the engine comprises a diesel engine, at least onediesel particulate filter (DPF) 72 may be coupled downstream of theemission control device 70 in order to trap soot. The DPF may bemanufactured from a variety of materials including cordierite, siliconcarbide, and other high temperature oxide ceramics. As such, the DPF mayhave a finite capacity for holding soot. Therefore, the DPF may beperiodically regenerated in order to reduce the soot deposits in thefilter so that flow resistance due to soot accumulation does not reduceengine performance. Filter regeneration may be accomplished by heatingthe filter to a temperature that will burn soot particles at a fasterrate than the deposition of new soot particles, for example, 400-600° C.In one example, the DPF may be a catalyzed particulate filter containinga washcoat of precious metal, such as platinum, to lower soot combustiontemperature and also to oxidize hydrocarbons and carbon monoxide tocarbon dioxide and water.

In an example where the engine may comprise a diesel engine, ahydrocarbon (HC) reductant delivery system 74 may be used to deliver HCfrom the fuel tank or from a storage vessel to the exhaust system togenerate heat for heating the particulate filter 72 for regenerationpurposes. Alternatively, or in addition, late fuel injection (e.g.,during an exhaust stroke) may be used to raise exhaust temperature.

Temperature sensors 76 and 78 may be located upstream and downstream,respectively of DPF 72, in the example case where the vehicle enginecomprises a diesel engine. The temperature sensors 76 and 78, oradditional temperature sensors, may also be located within the DPF, orDPF temperature (or exhaust temperature) may be estimated based onoperating conditions using an exhaust temperature model. A differentialpressure signal may be determined from pressure sensors 80 and 82upstream and downstream of DPF 72, respectively. Note that a singledifferential pressure may also be used to measure the differentialpressure across DPF 72. A single port gauge pressure sensor (SPGS) mayalso be used.

It should be appreciated that alternate emission control systemconfigurations may be used in alternate embodiments. For example,emission control device 70 may be coupled downstream of the DPF. Furtherin other examples, a plurality of diesel particulate filters may beincluded in the emission control system. Still further, in otherexamples the SCR catalyst may not be included in the emission controlsystem. Each catalyst, filter, etc., may be enclosed within a singlehousing or alternatively may be enclosed via separate housings. It willbe appreciated that numerous configurations are possible and theconfiguration depicted in FIG. 1 is exemplary in nature. Further still,as noted above, a reductant (e.g., ammonia or urea) injection system maybe coupled to the exhaust to inject urea upstream of emission controldevice 70.

To regenerate the DPF a regeneration injection strategy may beimplemented. The regeneration injection strategy may implement aninjection profile including a plurality of injection events such as apilot fuel injection, a main fuel injection, a near post fuel injection,and/or a far post fuel injection. It will be appreciated that theaforementioned fuel injections may include a plurality of injectionevents, in other embodiments. Thus, the DPF may be regenerated duringoperation of the engine. For example, the temperature downstream of aDOC and upstream of a DPF may be controlled to a desired value topromote combustion of particulate matter within the DPF, by adjustmentof the amount of the various injections. In this example, a temperatureset-point downstream of the DOC and upstream of the DPF may beestablished to facilitate regeneration of the DPF. In still furtherexamples, a heater 75 configured to raise temperature of the DPF may beutilized for DPF regeneration.

As discussed, regeneration of the DPF coupled to an underbody of a motorvehicle may include burning of particulate (e.g. soot) stored in theparticulate filter, which may result in hot gases exiting a rear (e.g.exhaust) of the motor vehicle. Thus, in some examples it may bedesirable to indicate whether an object is indicated to be below athreshold distance away from the exhaust. Such an object may beidentified via one or more onboard camera(s) (e.g. 186), and/or one ormore ultrasonic sensor(s) (e.g. 185), for example. In some examples,selecting an ultrasonic sensor to use in conducting a distancemeasurement between the sensor and an object may include selecting theselected sensor based on a transmission path of the selected sensoroverlapping at least a portion of the hot gases exiting the rear of themotor vehicle, and may further be based on the object being within atransmission path of the selected sensor as identified by one of thecameras. In such a case, if an object is indicated to be less than athreshold distance away from the exhaust (within a threshold distance ofthe hot gases exiting the rear of the motor vehicle), the DPFregeneration procedure may be postponed, or aborted, for example.Furthermore, ambient humidity and ambient temperature may affect thethermal conductivity of air, and thus in some examples it may bedesirable to obtain measurements of ambient temperature and humidity,such that a threshold distance that the object may be away from theexhaust may be adjusted according to the thermal conductivity of air.More specifically, in some examples, thermal conductivity of air may bedetermined based on an indication of relative humidity and airtemperature, where air temperature is measured near where the hot gasesexit the rear of the motor vehicle, and wherein adjusting the thresholddistance based on the measured thermal conductivity of air may includedecreasing the distance threshold as thermal conductivity decreases, andincreasing the distance threshold as thermal conductivity increases. Inthis way, DPF regeneration procedures may be commenced and completedmore frequently than if the distance threshold were not adjustable.Furthermore, responsive to an indication that an object is positioned ata greater distance than the threshold distance, the object and an areaproximate the rear of the vehicle may continue to be monitored duringconducting the regeneration procedure via the one or more cameras and/orultrasonic sensor(s). In such an example, if the object or other objectis identified as being closer than the adjusted threshold distanceduring the regeneration procedure, the regeneration procedure may beterminated.

Turning to FIG. 2, an exemplary parking assist system 200 employing theuse of an ultrasonic sensor 185 is schematically shown. The system 200includes components of a typical vehicle including a powertrain controlmodule 208 illustrated as a combined control unit consisting of thecontroller 12 and transmission control unit 210. The system 200 furtherincludes one or more ultrasonic sensor(s) 185, mounted on the vehicle invarious locations, and configured to provide inputs to a parkingassistance module 205. For example, ultrasonic sensors may be placed ona front, a side, a rear, or any combination of the front, rear, and/orside of the vehicle. Such a system 200 described in this disclosure isgenerally applicable to various types of vehicles, including small orlarge cars, trucks, vans, SUV's, etc., that may employ an ultrasonicsensor.

The term “power train” refers to a power generating and delivery systemthat includes an engine and a transmission, and is used as a drivesystem in an automotive vehicle. The power train control module 208performs engine and transmission control operations using a controller12 and a transmission control unit 210, respectively. The controller 12detects data from various portions of the engine and may adjust fuelsupply, ignition timing, intake airflow rate, and various other knownengine operations, as discussed above with regard to FIG. 1. Thetransmission control unit 210 detects engine load and vehicle speed todecide a gear position to be established in the transmission. For thepurpose of description, FIG. 2 depicts only a few components of thepower train control module 210. Those skilled in the art, however, willunderstand that the power train control module 208 may be operativelycoupled to a number of sensors, switches, or other known devices togather vehicle information and control various vehicle operations.

The parking assistance module 205 provides capabilities such asauto-parking, parallel parking, obstacle identification, and so on,resulting in a convenient or completely automatic parking process. Forexample, using the parking assistance module 205, the vehicle may steeritself into a parking space with little or no input from the driver. Inthat process the module detects and warns about objects that pose animpact risk. Detection and warning are performed by a number of sensors,such as the ultrasonic sensor 185, which cooperate to determine thedistance between the vehicle and surrounding objects. However, asdiscussed above and which will be discussed in further detail below,humidity may be a noise factor contributing to operational use of theultrasonic sensor. Accordingly, in some examples, relative humidity maybe determined via either the ultrasonic sensor itself, or via othersensors (e.g. UEGO sensor) in the vehicle, such that operational use ofthe ultrasonic sensor may be improved. In some examples, one or morecamera(s) positioned at one or more location on the vehicle may beutilized to detect objects of interest, such that a humidity calculationmay be conducted via the ultrasonic sensor(s), described in furtherdetail below. In such an example, a method may include selecting one ofa plurality of ultrasonic sensors positioned around a motor vehiclebased in part on one or more images from one or more cameras positionedaround the motor vehicle. The selected sensor may in some examples beselected based on an object, identified by one of the cameras, beingwithin a transmission path of the selected sensor. The object may insome examples be indicated to be stationary with respect to the vehicle.For example, it may be indicated via the cameras that the object isstationary, in some examples. In another example, the selected sensormay be selected based on there being a target vehicle traveling within atransmission path of the selected sensor and where the target vehicle istraveling at a velocity substantially equal to the motor vehiclevelocity and also at a substantially constant distance from the motorvehicle. Furthermore, in some examples, the one or more camera(s) mayfunction to additionally or alternatively communicate images and roughdistance indications (e.g. via object recognition analysis) during anassisted or fully automated parking procedure.

The ultrasonic sensor 185 may detect obstacles on either side, in thefront, or the rear of the vehicle, and vehicle modules, such as asteering wheel module (not shown), brake system (not shown), parkingassistance module (205), etc., may utilize such information. Thus, whilethe one or more ultrasonic sensor(s) 185 are illustrated coupled to theparking assistance module, such a depiction is for illustrative purposesonly, and is not meant to be limiting. For the sake of brevity, however,in-depth description of other potential uses of one or more ultrasonicsensor(s) will not be discussed herein. However, it may be understoodthat uses of the ultrasonic sensor(s) other than parking assistance maybe utilized according to the methods described herein, without departingfrom the scope of the present disclosure.

The one or more ultrasonic sensor(s) 185 may be configured to include atransmitting (sending) means, adapted to transmit ultrasonic waves, anda receiving means, adapted to receive the waves reflected from an objectin the vicinity of the vehicle, such as obstacle 220. A transit timecomprising a time between transmitting and receiving the ultrasonic wavesignal may be determined, and a distance between the sensor and theobstacle (for example) may be indicated based on the formula d=c*t/2,where c is the speed of sound and t is the transit time. This distanceinformation may then be provided to the parking assistance module 205(or other relevant module), for example. Such object detectioncapabilities of ultrasonic sensors are well known to those skilled inthe art and will not be discussed in detail in the present disclosure.

As discussed above, operational use of the one or more ultrasonicsensors 185 may be subject to noise factors. The four main noise factorsthat affect ultrasonic sensors are temperature, humidity, target surfaceangle, and reflective surface roughness. However, as will be discussedin further detail below, temperature may be compensated for by measuringair temperature. Furthermore, target surface angle and reflectivesurface roughness may be compensated for by the use of two or more wavefrequencies sent from a single transmitting means, where only reflectedsignals which have the same transit time from transmission to receiptare utilized to determine distance measurements, discussed in furtherdetail below. However, for vehicles without a dedicated humidity sensor,compensating for humidity may be challenging.

Thus, methods for determining, and compensating, for humidity via theuse of an ultrasonic sensor (e.g. 185), are described in further detailbelow with regard to FIGS. 4-7, FIG. 9, and FIGS. 11-12. Briefly,humidity differentially affects an amount of attenuation (e.g. loss inintensity) observed for different frequencies of sound. Thus, bytransmitting a plurality of ultrasonic frequencies from an ultrasonicsensor and determining attenuation of each of the individualfrequencies, relative humidity may be calculated as a function of thedifference in attenuation between the pairs of frequencies. However, insome examples, certain frequencies may be better suited for determiningdifferences in attenuation between pairs of frequencies. Accordingly,some examples may include changing frequencies of the transmittedsignals responsive to a determination that the reflected signals have,or would have, undesired signal-to-noise ratio(s).

For example, certain environmental conditions (e.g. wind, rain, snow,fog, temperature fluctuations, etc.), may affect a signal-to-noise ratioof particular frequencies. As such, if a particular frequency isindicated to have undesirable signal-to-noise, in other words,attenuation is too great, then one or more additional frequency(s) maybe transmitted and received such that only frequency(s) with desiredsignal-to-noise ratios may be utilized for conducting a relativehumidity measurement.

Thus, changing the frequency(s) of the transmitted signals may includechanging the frequency(s) responsive to environmental conditionsincluding one or more of the following: ambient temperature, ambienthumidity, and a transit time from transmission to receipt of thetransmitted and reflected signals.

For example, a previous humidity estimation may in some examples be usedas a reference for changing frequency(s) to achieve desiredsignal-to-noise ratios. As an example, if humidity is indicated tolikely be high based on a previous humidity estimation, where theprevious humidity estimation may be stored at the controller, then oneor more frequency(s) may be excluded and another frequency selected,where the selected frequency may be a frequency likely to exhibit adesired signal-to-noise ratio of the transmitted and received signal.

Similarly, in some examples, changing frequency(s) may be a function ofan indicated ambient temperature. In still further examples, changingfrequency(s) may be a function of indicated transit time fromtransmission to receipt of the transmitted and reflected signals. Forexample, if a transit time from transmission to receipt of thetransmitted and reflected signals is not within an expected range, thenit may be indicated that an environmental or other condition isaffecting signal-to-noise and/or integrity of the transmitted andreceived signal, and the frequency may be changed in an attempt toincrease the signal-to-noise ratio and/or the integrity of the signal.In one example, such a condition affecting transit time fromtransmission to receipt of the transmitted and reflected signals mayinclude a dirty ultrasonic sensor. Such an example may include comparingamplitude of the reflected signal to a reference amplitude based on adistance of an object from which the selected signal is reflected, andenvironmental conditions including, but not limited to, humidity ortemperature to determine whenever the sensor needs to be cleaned. In anexample where the sensor may need to be cleaned, changing frequency(s)may alleviate the issue. In still other examples, a different ultrasonicsensor (instead of the dirty ultrasonic sensor) may be selected, wherethe different ultrasonic sensor may be selected responsive to anindication that the transmission path of the ultrasonic sensor overlapswith an object of interest to be utilized for conducting a relativehumidity estimate. Said another way, in some examples selecting one of aplurality of sensors positioned around the motor vehicle may be based inpart on whether any of the plurality of sensors need to be cleaned.

Turning now to FIG. 3A, a graph 300 depicting sound attenuation as afunction of percent relative humidity, is shown. More specifically,percent relative humidity is illustrated on the x-axis, and soundattenuation in dB/km is illustrated on the y-axis. Line 302 indicatesultrasonic frequency at 100 kHz, line 304 indicates 80 kHz, line 306indicates 63 kHz, line 308 indicates 50 kHz, line 310 indicates 40 kHz,line 312 indicates 31.5 kHz, line 314 indicates 25 kHz, and line 316indicates 20 kHz. As illustrated, sound attenuation increases asultrasonic wave frequency increases.

Turning now to FIG. 3B, a graph 340 depicting sound attenuation as afunction of percent relative humidity is again illustrated. As in FIG.3A, line 302 indicates ultrasonic frequency at 100 kHz, and line 316illustrates ultrasonic frequency at 20 kHz. For illustrative purposes,arrow 342 is depicted, indicating the difference in attenuation at fortypercent relative humidity between ultrasonic frequency at 100 kHz and 20kHz.

Accordingly, turning to FIG. 3C, graph 360 is shown depicting adifference in sound attenuation 362 between 100 kHz and 20 kHz, acrossthe range of percent relative humidity indicated in FIGS. 3A-3B. Morespecifically, the difference in sound attenuation (delta soundattenuation) between 100 kHz and 20 kHz is illustrated on the x-axis,and percent relative humidity is indicated on the y-axis. By plottingdifferences in attenuation between two frequencies as a function ofpercent relative humidity, a simple transfer function, represented byarrows 364 may be used to determine relative humidity. Said another way,conversion of the difference in attenuation may comprise the use of atransfer function to convert the difference in attenuation into ameasurement of relative humidity. For example, a two dimensional (2D)lookup table may include known, or predetermined, values correspondingto relative humidity as a function of differences in sound attenuationbetween different frequencies. Once the difference in sound attenuationbetween two different frequencies is known, such a lookup table may beused to indicate relative humidity. While differences in soundattenuation are illustrated for 100 kHz and 20 kHz, it may be understoodthat the use of such frequencies to determine relative humidity are forillustrative purposes only, and differences in sound attenuation betweentwo frequencies corresponding to frequencies other than 100 kHz and 20kHz may be similarly utilized.

Turning to FIG. 4, a high level flowchart for an example method 400 fordetermining humidity via the use of an ultrasonic sensor, is shown. Morespecifically, method 400 may include transmitting a plurality of signalsfrom a single sensor, each at a different frequency, receiving reflectedsignals of the transmitted signals, and determining attenuation valuesonly for each of the reflected signals which have the same transit timefrom transmission to receipt. Responsive to determining attenuationvalues, method 400 may further include determining differences betweenpairs of the attenuation values, and converting the differences to anindication of relative humidity.

Method 400 will be described with reference to the systems describedherein and shown in FIG. 1 and FIG. 2, though it should be understoodthat similar methods may be applied to other systems without departingfrom the scope of this disclosure. Method 400 may be carried out by acontroller, such as controller 12 in FIG. 1, and may be stored at thecontroller as executable instructions in non-transitory memory.Instructions for carrying out method 400 and the rest of the methodsincluded herein may be executed by the controller based on instructionsstored on a memory of the controller and in conjunction with signalsreceived from sensors of the engine system, such as the sensorsdescribed above with reference to FIG. 1. The controller may employactuators, such as ultrasonic sensor (e.g. 185), etc., according to themethod below.

Method 400 begins at 405 and may include determining engine operatingparameters. Operating conditions may be estimated, measured, and/orinferred, and may include one or more vehicle conditions, such asvehicle speed, vehicle location, etc., various engine conditions, suchas engine status, engine load, engine speed, A/F ratio, etc., variousfuel system conditions, such as fuel level, fuel type, fuel temperature,etc., various evaporative emissions system conditions, such as fuelvapor canister load, fuel tank pressure, etc.

Continuing to 410, method 400 may include measuring ambient airtemperature. As discussed above with regard to FIG. 1, an outside airtemperature (OAT) sensor (e.g. 127) positioned on the exterior of thevehicle system (e.g. 101) may be used to determine ambient airtemperature. For example, controller (e.g. 12) may send a signal to OATsensor to take a reading of ambient air temperature. The reading maythen be communicated back to the controller, and may be stored at thecontroller, for example. As will be discussed in further detail below,knowledge of ambient air temperature may be taken into account whencalculating total attenuation difference between two given ultrasonicfrequencies. Said another way, converting distances between pairs ofattenuation values to an indication of relative humidity may rely onmeasured ambient air temperature.

Proceeding to 415, method 400 may include performing a VariableFrequency Algorithm (VFA), consisting of sending and receiving aplurality of ultrasonic frequencies, such that difference(s) inattenuation may be calculated. Performing the (VFA) may be conductedaccording to method 500, depicted in FIG. 5.

Accordingly, turning to FIG. 5, a high level flowchart for an examplemethod 500 for conducting the VFA, is shown. More specifically, method500 may include commanding the ultrasonic sensor to transmit anultrasonic wave (chirp signal) at a first frequency, and then measuringand storing a transit time and intensity of the resulting echo. Next,method 500 may include commanding the ultrasonic sensor to transmitanother chirp at a second frequency, and may further includesubsequently measuring and storing transit time and intensity of theresulting echo corresponding to the second chirp signal.

Method 500 will be described with reference to the systems describedherein and shown in FIG. 1 and FIG. 2, though it should be understoodthat similar methods may be applied to other systems without departingfrom the scope of this disclosure. Method 500 may comprise a sub-methodof method 400, and thus method 500 may be carried out by the controller(e.g. 12), and may be stored at the controller as executableinstructions in non-transitory memory. Instructions for carrying outmethod 500 and the rest of the methods included herein may be executedby the controller based on instructions stored on a memory of thecontroller and in conjunction with signals received from sensors of theengine system, such as the sensors described above with reference toFIG. 1. The controller may employ actuators, such as ultrasonic sensor(e.g. 185), etc., according to the method below.

Method 500 begins at 505 and may include transmitting a chirp signal ata first frequency. More specifically, the controller may command anelectronic signal in the form of an oscillated voltage to the ultrasonicsensor (e.g. 185), where the frequency of the oscillated voltage maycorrespond to the desired frequency of the resultant ultrasonic wave. Insome examples, the first frequency may comprise a frequency for which agreatest amount of attenuation would be expected, for example 100 kHz.However, such an example is illustrative and not meant to be limiting.Instead, any frequency between and including 20 kHz-100 kHz may be firsttransmitted.

Continuing to 510, method 500 may include measuring and storing thetransit time (t1) and intensity (i1) of the resulting echo correspondingto the transmitted chirp at the first frequency (f1). For example, theultrasonic sensor may be configured to convert the received echo(received sound wave) into an oscillating voltage, where an electricpotential of the oscillating voltage may correspond to the intensity ofthe ultrasonic wave. A decrease in intensity of the resulting echo maybe understood to be indicative of the attenuation of the ultrasonic wavefrom transmission to receipt.

Upon receiving the echo corresponding to the transmitted chirp signal atthe first frequency, method 500 may proceed to 515. At 515, method 500may include transmitting a chirp signal at a second frequency (f2).Importantly, it may be understood that the resultant echo of the firstfrequency may be first received by the ultrasonic sensor, prior tosending out the second chirp signal. The second chirp signal may bedifferent in frequency than the first chirp signal, and may correspondto a frequency greater than, or less than the first chirp signalfrequency. For example, if the first frequency (f1) was 100 kHz, thenthe second frequency (f2) may be 20 kHz. Such an example is illustrativeand is not meant to be limiting.

Proceeding to 520, similar to step 510, method 500 may include measuringand storing transit time (t2) and intensity (i2) of the resulting echocorresponding to the second chirp signal. As discussed above, transittime and intensity of the second chirp signal may be stored at thecontroller (e.g. 12).

Proceeding to 525, method 500 may include determining whether additionalaccuracy (e.g. better signal-to-noise) may be desired. For example,responsive to the sending and receiving of the first two ultrasonicwaves (chirp signals), the controller may determine whethersignal-to-noise of the received ultrasonic waves are sufficient (above apredetermined threshold level) for analysis. In some examples, dependingon a contour and/or reflective angle of an object that is reflecting thetransmitted waves, one or more of the received signals may be below athreshold desired for accurate measurement of attenuation. In anotherexample, environmental conditions (e.g. wind, rain, etc.) may result inone or more of the received signals being below the predeterminedthreshold level. In another example, environmental conditions mayinclude one or more of the following: ambient temperature, ambienthumidity, and the transit time from transmission to receipt of thetransmitted and the reflected signals. In still further examples, adirty ultrasonic sensor may result in one or more of the receivedsignals being below the predetermined threshold level.

In still other examples, additional accuracy may be desired based on theintended use of a humidity measurement via the ultrasonic sensor. As anexample, if a humidity estimation were previously indicated via anothermeans (e.g. UEGO, etc.), and the ultrasonic sensor is being used as acheck to verify that the prior measurement is, in fact, still correct, aprecisely accurate measurement may not be desired. In such an example,if the signal-to-noise of the echoes received from the transmitted firstand second frequencies is above the predetermined threshold, then onlytwo frequencies may be utilized for determining an estimation ofhumidity. However, there may be other examples where more precisemeasurements of relative humidity may be desired. Such an example mayinclude a condition where a duration of time has elapsed since aprevious humidity measurement, where a change in barometric pressure isindicated to have changed greater than a threshold amount, where achange in temperature is indicated to have changed greater than athreshold amount, wherein accurate humidity inference is desired forengine operation, or for parking assistance, etc.

In any of the above-mentioned examples, or other examples notspecifically mentioned, where additional accuracy is desired, method 500may proceed to 530. At 530, method 500 may include commanding theultrasonic sensor to transmit one or more additional chirp signals (e.g.change frequencies), each of which may be measured as described abovefor transit time and return echo intensity, by the ultrasonic sensor. Asan example, a third, fourth, and fifth frequency may be transmitted andeach monitored for transit time and return echo intensity. Such anexample is meant to be illustrative, and not meant to be limiting.However, it may be understood that accuracy of the resulting humiditymeasurement, which will be described in detail below, may be increasedwith increasing numbers of frequencies transmitted and received. Saidanother way, frequencies of the transmitted signals may be changedresponsive to a determination that the reflected signals have or wouldhave a desired signal-to-noise below a predetermined threshold level,and wherein changing frequencies of the transmitted signals occurs priorto determining differences between pairs of the attenuation values andconverting differences to an indication of relative humidity, as will bediscussed in further detail below.

Returning to 525, responsive to the two or more received frequenciesbeing of sufficient signal-to-noise for the desired accuracy of theresulting humidity measurement (described below), method 500 may returnto step 420 of FIG. 4.

At step 420 of FIG. 4, method 400 may include indicating whether transittimes for each of the frequencies are equivalent. For example, if twofrequencies were transmitted and received at step 415, then it may bedetermined whether the two frequencies both have the same transit time.If three frequencies were transmitted and received at step 415, then itmay be determined whether all three of the frequencies have the sametransit time, etc. In calculating differences in attenuation in order todetermine relative humidity, only those frequencies that have the sametransit times may be further processed, as will be discussed in furtherdetail below. More specifically, attenuation values may be determinedonly for each of the reflected signals which have the same transit timefrom transmission to receipt, which may correct for variations in targetsurface angle and reflective surface roughness, for example.

Accordingly, if it is indicated at step 420 that all of the transittimes for each of the frequencies transmitted and received at step 415are equivalent, method 400 may proceed to 425.

At 425, method 400 may include performing a Delta AttenuationCalculation (DAC) according to the method depicted in FIG. 6.

Turning now to FIG. 6, a high level example method 600 for performing aDAC, is shown. More specifically, frequencies that were transmitted andreceived according to the variable frequency algorithm (VFA) describedabove with regard to FIG. 5, and which were indicated to have the sametransit times described above with regard to FIG. 4, may be processed inorder to calculate attenuation of each of the individual frequencies,which may then be used to calculate differences in attenuation betweenfrequencies such that relative humidity may be determined.

Method 600 will be described with reference to the systems describedherein and shown in FIG. 1 and FIG. 2, though it should be understoodthat similar methods may be applied to other systems without departingfrom the scope of this disclosure. Method 600 may comprise a sub-methodof method 400, and thus method 600 may be carried out by the controller(e.g. 12), and may be stored at the controller as executableinstructions in non-transitory memory. Instructions for carrying outmethod 600 and the rest of the methods included herein may be executedby the controller based on instructions stored on a memory of thecontroller and in conjunction with signals received from sensors of theengine system, such as the sensors described above with reference toFIG. 1.

Method 600 begins at 605 and may include calculating attenuation (α) foreach frequency with equivalent transit times as indicated by method 400of FIG. 4. More specifically, calculating attenuation for a firstfrequency (f1) may be conducted based on the following formulaS1=S0*e^(−α1*z);  (1)where S0 is the original intensity of the non-attenuated signal, z isthe distance the signal travels, S1 is the intensity of the receivedattenuated signal, and α1 is the attenuation coefficient for frequencyf1.

Rearranging equation (1), givesAttenuation=α1=ln(S1/S0)/−z.  (2)A total attenuation coefficient (αTot) is comprised of attenuation dueto temperature, humidity, target surface angle, and reflective surfaceroughness. However, by conducting the VFA according to the methoddepicted in FIG. 5, and by further ensuring that only those frequencieswith the same transit times are processed for the DAC, as illustrated bythe method depicted in FIG. 4, the effects of temperature, targetsurface angle, and reflective surface roughness may be subtracted out.More specifically, because temperature is known its effect may becancelled out, and target surface angle and reflective surface roughnessdoes not change during differential measurement of frequency echointensity, provided that transit times for each of the frequenciesanalyzed are equivalent. Thus, of the variables that affect the totalattenuation coefficient (αTot), only humidity is not known and may havea different attenuation coefficient for different frequencies.

Accordingly, after all attenuation values have been calculated for eachof the analyzed frequencies at 605, method 600 may proceed to 610. At610, method 600 may include calculating the delta (Δ) attenuation valuesfor each of the analyzed frequencies. More specifically, deltaattenuation due to humidity between two frequencies, f1 and f2 forexample, may be equal to total delta attenuation between f1 and f2, forthe reasons described above. ThusΔαHumidity(f1−f2)=ΔαTotal(f1−f2)=Δα(f1−f2).  (3)As illustrated by equation 3, two frequencies f1 and f2 are shown.However, it may be understood that in an example where more than twofrequencies may be utilized in order to perform the VFA depicted in FIG.5, and the DAC depicted herein with regard to FIG. 6, each frequencyutilized may be subtracted from all other frequencies in order toincrease accuracy of the delta attenuation measurement. Taking threefrequencies as an example, where the three frequencies comprise f1, f2,and f3, the delta attenuation calculation may comprise (f1−f2), (f1−f3),and (f2−f3), where the differences may comprise absolute values of therespective differences. Similar methodology may apply to examples wheremore than three frequencies may be utilized.

Proceeding to 615, once Δattenuation has been calculated for each pairof frequencies, method 600 may include storing the Δattenuation valuesand corresponding frequency values into a table, where the table may bestored at the controller (e.g. 12). Method 600 may then return to step425 of method 400.

Accordingly, returning to step 425 of method 400, once the DAC has beenconducted according to method 600 depicted in FIG. 6, method 400 mayproceed to 430. At 430, method 400 may include determining relativehumidity using a lookup table stored at the controller. For example, asimple transfer function may be utilized such that, for a given pair offrequencies and a given Δattenuation for the given pair of frequencies,relative humidity may be determined by correlating the transfer functionwith the lookup table stored at the controller (see FIG. 3C). In a casewhere multiple Δattenuation values for multiple pairs of frequencies areobtained, each Δattenuation value and corresponding pair of frequenciesmay be used to obtain a percent relative humidity, and all the relativehumidity values may then be averaged by the controller in order toincrease confidence in the relative humidity measurement.

Returning to 420 of method 400, if it is indicated that not all of thetransit times for the frequencies utilized at step 415 are indicated tobe equivalent, method 400 may proceed to 435 and may include selectivelydiscarding non-equivalent data. For example, data corresponding tofrequencies that have the same transit times may be stored at thecontroller (e.g. 12), while data from frequencies without otherequivalent transit times may be discarded. Proceeding to 440, it may beindicated whether the remaining data set is sufficient for determininghumidity with the desired accuracy. As an example, if only twofrequencies were indicated to have the same transit times, but increasedaccuracy is desired, where the increased accuracy may comprisecalculating relative humidity from a data set comprising more than twofrequencies, then method 400 may proceed to 445. Thus, at 440, if it isindicated that the remaining data set is not sufficient for calculatingrelative humidity with the desired accuracy, method 400 may proceed to445 and may include determining humidity in another way, whereconditions allow. In some examples, determining humidity may beaccomplished via the use of intake or exhaust gas oxygen sensor(s), aswill be discussed with regard to FIGS. 8-9. Alternatively, if at 440, itis indicated that the remaining data set is sufficient for determiningrelative humidity with the desired accuracy, method 400 may proceed to425, and may include performing the DAC as described above.

In some examples, a vehicle may be equipped with a plurality ofultrasonic sensors. In such a case, there may be instances where it maybe beneficial to prioritize the use of a particular sensor whenconducting a relative humidity measurement. Such examples may include acondition where one or more sensors are indicated to be dirty, or notfunctioning as desired. In such a case, it may be beneficial to only usethe ultrasonic sensor(s) that are functioning as desired. In anotherexample, it may be beneficial to detect an object by a secondary means,and then preferentially use an ultrasonic sensor positioned in anoptimal location in order to increase the likelihood of a successfulrelative humidity determination. In some examples, detecting an objectby a secondary means may comprise detecting an object via the use of oneor more onboard camera(s) (e.g. 186).

For example, one or more camera(s) may be physically wired andcommunicatively coupled to a control system of the vehicle including acontroller (e.g. 12). In another example, one or more camera(s) may beadditionally or alternatively in wireless communication with thecontroller, for sending and receiving data transmissions. Wiredcommunication may comprise USB technology, IEEE 1394 technology, opticaltechnology, other serial or parallel port technology, or any othersuitable wired link. Additionally or alternatively, wirelesscommunication with the one or more camera(s) may comprise Bluetooth, anIEEE 802.11 protocol, an IEEE 802.16 protocol, a cellular signal, ashared Wireless Access Protocol-Cord Access (SWAP-CA) protocol, awireless USB protocol, or any other suitable wireless technology. Thecontroller may receive one or more data files from the one or morecameras, such as video data files, image data files, etc.

The one or more cameras may include cameras mounted on the front or rearbumper, or any other suitable location on the front or rear of thevehicle. In some examples, more than one camera may be mounted on thefront and/or rear. For example, two or more cameras may be mounted onthe front of the vehicle, and two or more cameras may be mounted on therear of the vehicle. Similarly, one or more side-facing cameras may bepositioned at any suitable location on the vehicle in order to imageobjects on either or both of a left side of the vehicle, and a rightside of the vehicle. In some examples, more than one camera may beutilized to capture images corresponding to the left side of thevehicle, and more than one camera may be utilized to capture imagescorresponding to the right side of the vehicle.

In some examples, the one or more cameras may be fixed, while in otherexamples the one or more cameras may be moveable or rotatable relativeto the vehicle. Further, some examples may include one or more fixedcameras, and one or more moveable cameras. Position of the one or morecameras on the vehicle may in some examples enable 360° viewingcapabilities. As discussed, the one or more cameras may include camerasfor capturing videos and/or images. In other examples, the one or morecameras may comprise infrared cameras. Some implementations may includea plurality of cameras, some of which may be configured for capturingimage and/or video, while one or more other cameras may be configured tocapture infrared images.

In some examples, the one or more cameras may be configured to detectobjects in the vicinity of the vehicle. For example, object detectionsystems (often referred to as obstacle detection systems) that operatevia the use of one or more vehicle cameras, are well known in the art.More specifically, vehicle safety systems are widely known that enabledetection of obstacles such as pedestrians, bicycles, road blocks, othercars, etc. An in depth discussion of all possible variations of objectrecognition via the use of one or more camera(s) is outside the scope ofthe present disclosure. However, it may be understood that any methodknown by those skilled in the art may be utilized to conduct objectrecognition via the use of one or more camera(s), as will be discussedin further detail below. As an illustrative example, one method ofobject recognition may include edge detection techniques, such as theCanny edge detection, to find edges in an image frame acquired by theone or more cameras. An edge-image corresponding to the image frame maythen be generated. Furthermore, a binary image corresponding to theedge-image may also be generated. Subsequently, one or more “blobs” inthe binary image corresponding to one or more objects, or obstacles, maybe identified. Based on an analysis of the blobs in the binary image,information such as shape, relative size, relative distance, etc., ofeach of the blobs corresponding to objects may be determined. Asdiscussed, such an example is meant to be illustrative, and in no waylimiting. Other methods and systems for object detection via the use ofone or more cameras that are known in the art may be readily utilizedwithout departing from the scope of the present disclosure.

In some examples, object detection via the one or more cameras may becarried out while the vehicle is stationary. In other examples, objectdetection via the one or more cameras may be carried out while thevehicle is in motion. In either example, identified objects may beindicated to be stationary with respect to the vehicle if the identifiedobject does not change in position, size, or shape, over a particulartime period. For example, multiple images may be captured from the oneor more cameras over a predetermined time period, and if position, size,and shape of a particular identified object does not change over thepredetermined time period, it may be indicated that the identifiedobject is stationary with respect to the vehicle. In one example, suchan object that may be stationary with respect to the vehicle may beanother vehicle traveling either in front of, on a left or right sideof, or in back of, where both vehicles are traveling at substantiallythe same velocity and direction. As will be discussed below,identification of stationary objects with respect to the vehicle may beutilized in order to select from a plurality of ultrasonic sensorspositioned on the vehicle, in order to conduct relative humiditymeasurements with increased likelihood of attaining accuratemeasurements.

Turning now to FIG. 7, a high level example method for detecting objectswith one or more available cameras positioned on a vehicle, such that anultrasonic sensor may be selected to conduct a relative humiditymeasurement, is shown. More specifically, one or more cameras may beconfigured to search an environment surrounding (e.g. proximal) thevehicle for objects that are stationary with respect to the vehicle.Responsive to identification of a suitable object, an ultrasonic sensormay be selected from a plurality of ultrasonic sensors positioned on thevehicle, to conduct a relative humidity measurement. In this way, arelative humidity measurement may be conducted with an increasedlikelihood of an accurate measurement of relative humidity beingattained, and without unnecessary use of ultrasonic sensors underconditions where an accurate relative humidity measurement is notlikely. By obtaining accurate relative humidity measurements, certainvehicle operating procedures, such as assisted or fully automatedparking features, an amount of exhaust gas recirculation, an amount ofspark retard, etc., may be more effectively controlled.

Method 700 will be described with reference to the systems describedherein and shown in FIG. 1 and FIG. 2, though it should be understoodthat similar methods may be applied to other systems without departingfrom the scope of this disclosure. Method 700 may be carried out by acontroller (e.g. 12), and may be stored at the controller as executableinstructions in non-transitory memory. Instructions for carrying outmethod 700 and the rest of the methods included herein may be executedby the controller based on instructions stored on a memory of thecontroller and in conjunction with signals received from sensors of theengine system, such as the sensors described above with reference toFIG. 1. The controller may employ actuators, such as ultrasonic sensor(e.g. 185), one or more onboard camera(s) (e.g. 186), etc., according tothe method below.

Method 700 begins at 705 and may include searching an environment aroundthe vehicle with available cameras on the vehicle, in order to detectobjects suitable for conducting a relative humidity measurement. In someexamples, searching the environment with available cameras may commenceresponsive to one or more conditions triggering a desired humiditymeasurement. For example, conditions triggering a humidity measurementmay include an indicated change in ambient temperature greater than anambient temperature threshold since a previous (e.g. last) humiditymeasurement. Another example may include a change in ambient pressuregreater than an ambient pressure threshold since a previous (e.g. last)humidity measurement. Still other examples may include an indication ofa change in weather conditions, indicated by activation of windshieldwipers (not shown), as an example. More specifically, responsive toactivation of the vehicle windshield wipers, a signal may be sent to thecontroller requesting a relative humidity measurement, which may includethe controller first commanding the one or more cameras to scan theenvironment for suitable objects.

In still other examples, searching the environment with availablecameras may commence responsive to a threshold time of engine operationelapsing, or responsive to a distance of vehicle travel being greaterthan a predetermined distance since a previous (e.g. last) humiditymeasurement.

As discussed above, in some examples the vehicle may be equipped with anonboard navigation system (GPS) (e.g. 34) that includes one or morelocation sensors for assisting in estimating vehicle speed, vehiclealtitude, vehicle position/location, etc. Such information may be usedto infer local barometric pressure, for example, where a change in localbarometric pressure greater than a threshold since a previous humiditymeasurement may trigger a request for a new humidity measurement, wheresuitable objects may be determined via onboard camera(s). In stillfurther examples, the controller (e.g. 12) may be configured to receiveinformation via the internet or other communication networks.Information received from the GPS may, in some examples, becross-referenced to information available via the internet to determinelocal weather conditions, etc. In some examples, a change in weatherconditions as indicated by GPS and cross-referenced to the internet maytrigger a request for a relative humidity measurement, where availablecamera(s) may be utilized to scan the environment for suitable objectsfor conducting the relative humidity measurement.

In still further examples, there may be conditions of vehicle operationwhere the one or more available camera(s) are in operation (e.g. assistor fully-automated parking maneuvers), and where a relative humiditydetermination may be opportunistically conducted. As an example, if avehicle is conducting a parking maneuver, where the parking maneuverinvolves the use of one or more onboard camera(s), if the camera(s)detect a suitable object for conducting a relative humidity measurement,a relative humidity measurement may be conducted, described in furtherdetail below.

Accordingly, if conditions are met for searching the environment inproximity to the vehicle for suitable objects for conducting a relativehumidity measurement, then at 705 of method 700, the one or more camerasmay be activated in order to search for suitable objects. Specifically,a command may be sent from the controller (e.g. either a wired orwireless signal) to the one or more camera(s) to acquire one or moreimages of the environment around the vehicle. Images acquired by the oneor more camera(s) may be stored at the controller, for example, forfurther processing, described in detail below. In some examples whereone or more camera(s) are rotatable (e.g. movable, not fixed), thecontroller may be configured to capture images at different cameraangles, such that the environment surrounding the vehicle may beaccurately surveyed for suitable objects.

Discussed herein, suitable objects for conducting a relative humiditymeasurement may include but are not limited to objects above apredetermined threshold size, objects with a predetermined shape,objects that are indicated to be stationary with respect to the vehicle,objects with an indicated lack of surface roughness (e.g. smoothsurface), objects with a preferred angle of orientation, etc. Suitableobjects may further include objects that are likely to reflect anultrasonic signal back to an ultrasonic sensor, such that the transittime from transmission to receipt of the signal may be the same for aplurality of individual ultrasonic frequencies.

Accordingly, responsive to a request to search the environment forsuitable objects for conducting a relative humidity measurement, andresponsive to acquiring images via the one or more camera(s) at step705, method 700 may proceed to 710.

At 710, method 700 may include indicating whether suitable objects aredetected by the one or more camera(s). As discussed above, objectrecognition analysis may be conducted by the controller using any meansknown in the art on images acquired from the one or more camera(s), inorder to determine whether objects suitable for a relative humiditymeasurement are detected. In some examples, if multiple cameras areutilized in order to search the environment for suitable objects, thecontroller may process images from all of the cameras, and may furtheridentify a best or most suitable object for conducting a relativehumidity measurement. For example, in an example case where two camerasare utilized to search the environment, and where a suitable object isdetected from both cameras, it may be further determined what object ismost suitable for conducting a relative humidity test. One object beingmore suitable than another may include, but is not limited to, an objectbeing larger in size than another object, an object having less surfaceroughness than another object, an object more stationary than anotherobject with respect to the vehicle, etc.

Accordingly, if at 710, one or more suitable objects for conducting arelative humidity estimation are detected by the one or more camera(s),then method 700 may proceed to 715. At 715, method 700 may includeindicating the suitable objects' position with respect to the vehicle.For example, indicating the suitable objects' position with respect tothe vehicle may comprise indicating a position that the camera wasfacing at the time of image acquisition of the suitable object, anddetermining the location of the object as a function of direction thecamera was facing. In some examples, one or more camera sensors (e.g.187) may be used to send signals to the controller, indicating positionof the one or more cameras. The controller may be configured to processthe information on camera position, and based on an indication of cameraposition, a position of an identified suitable object relative to thevehicle may be indicated.

Proceeding to 720, method 700 may include indicating whether a vehicleis equipped with an ultrasonic sensor positioned to detect theidentified suitable object for conducting a relative humiditymeasurement. For example, if the vehicle is equipped with a plurality ofultrasonic sensors, then a position and location of one or more of theultrasonic sensors may be not be optimal for determining relativehumidity based on the position of the identified suitable object.Accordingly, those ultrasonic sensors that are not optimally positionedmay be excluded from conducting a relative humidity measurement. Inother words, at 720, it may be determined which of a plurality ofvehicle ultrasonic sensors is optimally positioned to conduct a relativehumidity measurement based on the position of the identified suitableobject. If, at 720, none of the available ultrasonic sensors areoptimally positioned to conduct a relative humidity measurement based onthe position of the identified suitable object with respect to thevehicle, then method 700 may return to 705, and may include continuingto search the environment surrounding the vehicle for suitable objects.In such an example, the identified suitable object for which anultrasonic sensor was not available may be excluded from furtheranalysis, such that only other suitable objects may be indicated inorder to identify a suitable object for which an ultrasonic sensor isoptimally positioned to conduct a relative humidity measurement.

In some examples, at 720, it may further be indicated as to whether theidentified optimal ultrasonic sensor is functioning as desired. Forexample, if an ultrasonic sensor is identified as being optimal fordetecting a particular identified suitable object, but that ultrasonicsensor is not functioning as desired, then method 720 may similarlyreturn to step 705, and may include continuing to search for suitableobjects with available cameras on the vehicle. In some examples, aparticular ultrasonic sensor may be indicated to not be functioning asdesired if it is dirty. A dirty ultrasonic sensor may be indicated, forexample, based on amplitude and distance of a reflected signal. Forinstance, a transmitted signal that travels less than an expecteddistance prior to being reflected back to be received by the sensor maybe indicative of a dirty ultrasonic sensor. Other examples of anultrasonic sensor that is not functioning as desired may include anyindication that function of the ultrasonic sensor is compromised.Illustrative examples may include an ultrasonic sensor with faultywiring, degraded components, etc. Accordingly, if, at 720, the optimalultrasonic sensor for detecting a particular suitable object isindicated to not be functioning as desired, then the cameras may befurther utilized in order to identify a suitable object for conducting arelative humidity test, for which there is an optimal humidity sensorpresent on the vehicle, and where the optimal humidity sensor isfunctioning as desired. In some examples, discussed above, more than onesuitable object may have been indicated at step 710. In such an example,if it is indicated that a particular ultrasonic sensor is notfunctioning as desired, then it may be further indicated as to whether adifferent ultrasonic sensor may be utilized to conduct a relativehumidity measurement on the other (e.g. one or more) suitable object(s).In such an example, if another ultrasonic sensor is indicated to beoptimally positioned to conduct a relative humidity measurement onanother identified suitable object, and it is further indicated thatsuch an ultrasonic sensor is functioning as desired, then it may bedetermined by the controller to employ the ultrasonic sensor that isfunctioning as desired to detect the indicated suitable object.

Accordingly, at step 720, responsive to an indication that a particularvehicle ultrasonic sensor is optimally configured to conduct a relativehumidity measurement based on a position of an identified suitableobject, where the suitable object is identified via one or more onboardcameras, method 700 may proceed to step 725. At step 725, method 700 mayinclude conducting the relative humidity measurement, as described abovewith regard to the methods depicted in FIGS. 4-6. Method 700 may thenend.

As discussed above, certain conditions may trigger a humiditymeasurement. Furthermore, in some examples, it may be preferable toconduct a humidity measurement utilizing an ultrasonic sensor, whereasin other examples it may be preferable to conduct a humidity measurementusing an alternate approach, such as via the use of a universal exhaustgas oxygen (UEGO) sensor. Such an example may include conditions where avehicle is in operation and one or more onboard camera(s) do notindicate any objects that are stationary with respect to the vehicle(e.g. no other vehicles traveling at essentially the same speed anddirection). In another example, optimal conditions for a humiditymeasurement using a UEGO sensor may be present, such as a decelerationfuel shut off (DFSO) event. In such an example it may be preferable toestimate relative humidity via the UEGO sensor, as will be described infurther detail below. By enabling humidity measurements based on vehicleoperating conditions, reliable humidity measurements may be obtained attimes when it is desirable to obtain humidity measurements.

Turning now to FIG. 8 a schematic view of an example embodiment of anexhaust gas oxygen sensor, such as UEGO sensor 800, configured tomeasure a concentration of oxygen (O₂) in an exhaust gas stream duringfueling conditions. In one example, UEGO sensor 800 is an embodiment ofUEGO sensor 126 of FIG. 1. It will be appreciated, however, that thesensor of FIG. 8 may alternatively represent an intake oxygen sensor,such as sensor 172 of FIG. 1. The exhaust gas oxygen sensor may also beused during non-fueled conditions to estimate an ambient humidity.Non-fueling conditions may include engine operating conditions in whichthe fuel supply is interrupted but the engine continues spinning and atleast one intake valve and one exhaust valve are operating; such as adeceleration fuel shut off (DFSO) event. Thus, air may be flowingthrough one or more of the cylinders, but fuel is not injected in thecylinders. Under non-fueling conditions, combustion is not carried outand ambient air may move through the cylinder from the intake passage tothe exhaust passage. In this way, a sensor, such as an exhaust gasoxygen sensor, may receive ambient air and ambient humidity may beestimated. In still other examples, an oxygen sensor disposed in theintake air passage (such as oxygen sensor 172 in FIG. 1), and/or adedicated humidity sensor may be used to estimate ambient humidityduring suitable conditions.

Sensor 800 comprises a plurality of layers of one or more ceramicmaterials arranged in a stacked configuration. In the embodiment of FIG.8, five ceramic layers are depicted as layers 801, 802, 803, 804, and805. These layers include one or more layers of a solid electrolytecapable of conducting ionic oxygen. Examples of suitable solidelectrolytes include, but are not limited to, zirconium oxide-basedmaterials. Further, in some embodiments such as that shown in FIG. 8, aheater 807 may be disposed in thermal communication with the layers toincrease the ionic conductivity of the layers. While the depicted UEGOsensor 800 is formed from five ceramic layers, it will be appreciatedthat the UEGO sensor may include other suitable numbers of ceramiclayers.

The layer 802 includes a material or materials creating a diffusion path810. The diffusion path 810 is configured to introduce exhaust gasesinto a first internal cavity 822 via diffusion. The diffusion path 810may be configured to allow one or more components of exhaust gases,including but not limited to a desired analyte (e.g., O₂), to diffuseinto the internal cavity 822 at a more limiting rate than the analytecan be pumped in or out by pumping electrodes pair 812 and 814. In thismanner, a stoichiometric level of O₂ may be obtained in the firstinternal cavity 822.

The sensor 800 further includes a second internal cavity 824 within thelayer 804 separated from the first internal cavity 822 by the layer 803.The second internal cavity 824 is configured to maintain a constantoxygen partial pressure equivalent to a stoichiometric condition, e.g.,an oxygen level present in the second internal cavity 824 is equal tothat which the exhaust gas would have if the air-fuel ratio wasstoichiometric. The oxygen concentration in the second internal cavity824 is held constant by pumping current I_(cp). Herein, the secondinternal cavity 824 may be referred to as a reference cell.

A pair of sensing electrodes 816 and 818 is disposed in communicationwith first internal cavity 822 and the reference cell 824. The sensingelectrodes pair 816 and 818 detects a concentration gradient that maydevelop between the first internal cavity 822 and the reference cell 824due to an oxygen concentration in the exhaust gas that is higher than orlower than the stoichiometric level.

The pair of pumping electrodes 812 and 814 is disposed in communicationwith the internal cavity 822, and is configured to electrochemicallypump a selected gas constituent (e.g., O₂) from the internal cavity 822through the layer 801 and out of the sensor 800. Alternatively, the pairof pumping electrodes 812 and 814 may be configured to electrochemicallypump a selected gas through the layer 801 and into the internal cavity822. Herein, the pumping electrodes pair 812 and 814 may be referred toas an O₂ pumping cell. The electrodes 812, 814, 816, and 818 may be madeof various suitable materials. In some embodiments, the electrodes 812,814, 816, and 818 may be at least partially made of a material thatcatalyzes the dissociation of molecular oxygen. Examples of suchmaterials include, but are not limited to, electrodes containingplatinum and/or gold.

The process of electrochemically pumping the oxygen out of or into theinternal cavity 822 includes applying an electric current I_(p) acrossthe pumping electrodes pair 812 and 814. The pumping current I_(p)applied to the O₂ pumping cell pumps oxygen into or out of the firstinternal cavity 822 in order to maintain a stoichiometric level ofoxygen in the cavity pumping cell. The pumping current I_(p) isproportional to the concentration of oxygen in the exhaust gas. Thus, alean mixture will cause oxygen to be pumped out of the internal cavity822 and a rich mixture will cause oxygen to be pumped into the internalcavity 822.

A control system (not shown in FIG. 8) generates the pumping voltagesignal V_(p) as a function of the intensity of the pumping current I_(p)required to maintain a stoichiometric level within the first internalcavity 822.

It should be appreciated that the oxygen sensor described herein ismerely an example embodiment of a UEGO (or intake manifold oxygen)sensor, and that other embodiments of intake or exhaust oxygen sensorsmay have additional and/or alternative features and/or designs. Asdiscussed briefly above and which will be described in detail below,under certain conditions it may be preferable to obtain humiditymeasurements via a UEGO or intake manifold sensor, while in otherconditions it may be preferable to obtain humidity measurements via anultrasonic sensor.

Turning now to FIG. 9 a high level example method 900 for conducting anopportunistic humidity measurement is shown. More specifically,responsive to conditions for a humidity determination procedure beingmet, a humidity determination may be conducted via either an oxygensensor, or via the use of an ultrasonic sensor. Method 900 will bedescribed with reference to the systems described herein and shown inFIGS. 1-2 and FIG. 8, and with reference to the methods described hereinand shown in FIGS. 4-7, though it should be understood that similarmethods may be applied to other systems without departing from the scopeof this disclosure. Method 900 may be carried out by a controller, suchas controller 12 in FIG. 1, and may be stored at the controller asexecutable instructions in non-transitory memory. Instructions forcarrying out method 900 and the rest of the methods included herein maybe executed by the controller based on instructions stored on a memoryof the controller and in conjunction with signals received from sensorsof the engine system, such as the sensors described above with referenceto FIG. 1 and FIG. 8. The controller may employ fuel system actuatorssuch as ultrasonic sensor(s) (e.g. 185), camera(s) (e.g. 186), oxygensensor(s) (e.g. 126), etc., according to the method below.

Method 900 begins at 902 and may include estimating and/or measuringcurrent vehicle operating parameters. Parameters assessed may include,for example, engine load, engine speed, vehicle speed, manifold vacuum,throttle position, spark timing, EGR flow, exhaust pressure, exhaustair/fuel ratio, assisted or fully-automated parking operations, etc.

Continuing to 905, method 900 may include indicating whether conditionsare met for conducting a humidity determination procedure. As discussedabove, conditions triggering a humidity measurement may include a changein ambient temperature greater than an ambient temperature threshold,and/or a change in ambient pressure greater than an ambient pressurethreshold, where the change in temperature and/or pressure is withrespect to a previous (e.g. last, or immediately preceding) humiditymeasurement. For example, ambient temperature may be directly estimatedas the outside air temperature (OAT) from an OAT sensor located on theexterior of the vehicle. In another example, ambient temperature may beinferred based on an air charge temperature (ACT) or an intake airtemperature (IAT), as measured by an IAT sensor coupled to an engineintake passage. Ambient pressure may be estimated based on the output ofa barometric pressure (BP) sensor coupled to the intake passage. In someexamples, instead of an absolute change in temperature or pressuredifference, it may be determined if the temperature or pressure haschanged by more than a threshold change in percentage (%), wherein thethreshold change in percentage may be adjusted based upon the absoluteambient temperature or pressure.

In another example, humidity determination conditions being met mayfurther include a threshold of time of engine operation or distance ofvehicle travel greater than a threshold distance since the last humiditymeasurement.

Other examples where humidity determination conditions may be met mayinclude activation of windshield wipers, a change in weather conditionsas indicated by GPS and cross-referenced to the internet, or any otherindication that ambient humidity may have changed since the lasthumidity measurement.

If, at 905 it is indicated that humidity determination conditions arenot met, method 900 may proceed to 910. At 910, method 900 may includecontinuing to adjust vehicle operating parameters based on the lasthumidity measurement obtained. For example, the last humiditymeasurement obtained may comprise a humidity measurement conducted viathe use of an exhaust gas oxygen sensor, or via an ultrasonic sensor.However, if, at 905 it is indicated that humidity determinationconditions are met, method 900 may proceed to 915. At 915, method 900may include indicating whether conditions are met for determininghumidity via either intake or exhaust oxygen sensors.

Conditions being met for a humidity determination via use of an exhaustgas oxygen sensor (e.g. UEGO) may include an engine-non fuelingcondition, such as a deceleration fuel shutoff (DFSO) event, where anambient humidity estimate may include alternating between applying firstand second voltages to the exhaust gas sensor, and generating anindication of ambient humidity based on sensor outputs at the first andsecond voltages, as described above with regard to FIG. 8.Alternatively, conditions being met for humidity determination via useof an intake oxygen sensor may include conditions where each of boost,exhaust gas recirculation (EGR), canister purging, and crankcaseventilation, are disabled, and where applying first and second voltagesto the intake oxygen sensor may enable an indication of ambient humiditybased on sensor output at the first and second voltages, as describedabove with regard to FIG. 8.

If, at 915, it is indicated that conditions are met for using intake orexhaust gas oxygen sensor(s) for a humidity estimation, then method 900may proceed to 920. At 920, method 900 may include determining humidityvia the intake or exhaust oxygen sensor.

If an exhaust passage UEGO sensor is used for humidity measurement, itmay be advisable to wait for a certain specified duration since fuelshut off until the exhaust is substantially free of hydrocarbons fromcombustion in the engine, before the humidity measurement is commenced.For example, residual gases from one or more previous combustion cyclesmay remain in the exhaust for several cycles after fuel is shut off andthe gas that is exhausted from the chamber may contain more than ambientair for a duration after fuel injection is stopped. In some examples,the duration since fuel shut off may be a time since fuel shut off. Inother examples, the duration since fuel shut off may be a number ofengine cycles since fuel shut off, for example.

For measuring humidity of the air, the sensor (intake sensor or exhaustsensor) modulates the reference voltage across the pumping cell betweena first voltage and a second voltage. Initially, a first (lower) pumpingvoltage may be applied. As one non-limiting example, the first voltagemay be 450 mV. At 450 mV, for example, the pumping current may beindicative of an amount of oxygen in the passage. At this voltage, watermolecules may remain intact, thus not contributing towards the totaloxygen present in the system. Next, a second (higher) pumping voltagemay be applied. As one non-limiting example, the second voltage may be950 mV. At the higher voltage, water molecules may be dissociated. Thesecond voltage is higher than the first voltage, wherein the secondvoltage dissociates water molecules and the first voltage does not, andwherein the sensor outputs include a first pumping current generatedresponsive to applying the first voltage and a second pumping currentgenerated responsive to applying the second voltage. Once the watermolecules are dissociated due to the second voltage, the total oxygenconcentration increases. The pumping current is indicative of the amountof oxygen in the passage plus an added amount of oxygen from dissociatedwater molecules. For example, the first voltage may be a voltage atwhich a concentration of oxygen may be determined, while the secondvoltage may be a voltage at which water molecules may be dissociated,enabling estimation of humidity.

Accordingly, a change in pumping current during the voltage modulationmay next be determined. An indication of ambient humidity may begenerated based on a difference between the first and second pumpingcurrent generated upon applying the first and second voltages,respectively. The difference (delta) in pumping current at the firstreference voltage and the pumping current at the second referencevoltage may be determined. The delta pumping current may be averagedover the duration of the DFSO condition (or other condition as describedabove) such that an ambient humidity may be determined. Once the averagechange in pumping current is determined, an estimation of ambienthumidity may be determined.

Subsequent to estimation of ambient humidity at 920, method 900 mayproceed to 925. At 925, method 900 may include adjusting vehicleoperating parameters based on the recent humidity measurement. Asnon-limiting examples, adjusting vehicle operating parameters mayinclude adjusting one or more of an amount of exhaust gas recirculation,an amount of spark advance or retard, a borderline spark value, and afuel octane estimate. For example, an increase in water concentration ofthe air surrounding the vehicle may dilute a charge mixture delivered toa combustion chamber of the engine. If one or more operating parametersare not adjusted in response to the increase in humidity, engineperformance and fuel economy may decrease and emissions may increase;thus, the overall efficiency of the engine may be reduced. In someembodiments, only one parameter may be adjusted responsive to thehumidity. In other embodiments, any combination or sub-combination ofthese operating parameters may be adjusted in response to measuredfluctuations in ambient humidity.

In one example embodiment, an amount of EGR may be adjusted based on themeasured humidity. For example, an increase in humidity may be detectedby the exhaust gas oxygen sensor during engine non-fueling conditions(or in other examples, by the ultrasonic sensor, as will be discussedbelow). In response to the increased humidity, during subsequent enginefueling operation, the EGR flow into at least one combustion chamber maybe reduced. As a result, engine efficiency may be maintained withoutdegrading NOx emissions. More specifically, a vehicle may be propelledat least in part by an engine comprising an intake manifold and anexhaust manifold, where the engine operates by combustion of fuelprovided to the engine, where an amount of exhaust gas recirculated tothe intake manifold of the engine is controlled while the engine isoperating, and where vehicle operating conditions may be adjustedresponsive to an indication of relative humidity, where the adjustingvehicle operating parameters includes one of at least an amount ofexhaust gas recirculation provided to the engine, and an amount by whichspark provided to the fuel for combustion is retarded or advanced(discussed below).

Responsive to a fluctuation in humidity, EGR flow may be increased ordecreased in at least one combustion chamber. As such, the EGR flow maybe increased or decreased in only one combustion chamber, in somecombustion chambers, or in all combustion chambers. Furthermore, amagnitude of change of the EGR flow may be the same for all cylinders orthe magnitude of change of the EGR flow may vary by cylinder based onthe specific operating conditions of each cylinder.

In another embodiment, spark timing may be adjusted responsive to thehumidity determination. In at least one condition, for example, sparktiming may be advanced in one or more cylinders during subsequent enginefueling operation responsive to a higher humidity determination. Inanother example, spark timing may be scheduled so as to reduce knock inlow humidity conditions (e.g., retarded from a peak torque timing), forexample. When an increase in humidity is detected via the humiditydetermination, spark timing may be advanced in order to maintain engineperformance and operate closer to or at a peak torque spark timing.

Additionally, spark timing may be retarded in response to a decrease inhumidity. For example, a decrease in ambient humidity from a higherhumidity may cause knock. If the decrease in humidity is detected by anexhaust gas sensor during non-fueling conditions, such as DFSO, sparktiming may be retarded during subsequent engine fueling operation andknock may be reduced. It should be noted that spark may be advanced orretarded in one or more cylinders during subsequent engine fuelingoperation. Further, the magnitude of change of spark timing may be thesame for all cylinders or one or more cylinders may have varyingmagnitudes of spark advance or retard.

In still another example embodiment, exhaust gas air fuel ratio may beadjusted responsive to the measured ambient humidity during subsequentengine fueling operation. For example, an engine may be operating with alean air fuel ratio (relative to stoichiometry) optimized for lowhumidity. In the event of an increase in humidity, the mixture maybecome diluted, resulting in engine misfire. If the increase in humidityis detected by the exhaust gas sensor during non-fueling conditions,however, the air fuel ratio may be adjusted so that the engine willoperate with a less lean air fuel ratio during subsequent fuelingoperation. Likewise, an air fuel ratio may be adjusted to be a more lean(than stoichiometry) air fuel ratio during subsequent engine fuelingoperation in response to a measured decrease in ambient humidity. Inthis way, conditions such as engine misfire due to humidity fluctuationsmay be reduced. In some examples, an engine may be operating with astoichiometric air fuel ratio or a rich air fuel ratio. As such, the airfuel ratio may be independent of ambient humidity and measuredfluctuations in humidity may not result in an adjustment of air fuelratio.

Furthermore, as described above, for a vehicle relying on one or moreultrasonic sensor(s) for conducting operations including parking assist,fully automated parking features, or other features, changes in humiditymay play a role in the operational use of the ultrasonic sensor.Accordingly, adjusting vehicle operating parameters based on the recenthumidity measurement at 925 may further include adjusting a distancedetection threshold for the ultrasonic sensor(s). For example, suitablefrequencies may be indicated for conducting a distance measurement,where the suitable frequencies are a function of the humiditydetermination. For example, certain frequencies may be attenuated moregreatly as percent relative humidity is increased. Such frequencies maythus be excluded from being utilized for conducting distancemeasurements, for example. Accordingly, a distance detection thresholdfor individual frequencies based on the determined ambient humidity maybe indicated, and stored in a lookup table at the controller, forexample. By adjusting a distance detection threshold for variousfrequencies of the ultrasonic sensor based on the determined humidity,operational use of the one or more ultrasonic sensor(s) may be improved.Such a concept will be further discussed below with regard to FIG. 11and FIG. 12.

Furthermore, in some examples, at step 925, tuning detection thresholdsmay be dynamically adjusted responsive to the indication of humidity.Adjusting tuning detection thresholds may comprise adjusting a voltagelevel (e.g. voltage response from the ultrasonic sensor) indicative ofan object, as compared to noise. More specifically, if tuning detectionthresholds are set too high, the sensor may be blind to may objects.Alternatively, if tuning detection thresholds are set too low, thesensor may be overly sensitive to noise, where an object may beindicated where, in fact, there is not object, for example. As humiditymay affect attenuation of ultrasonic waves in a frequency-dependentmanner, once humidity is known, tuning detection thresholds may beadjusted to account for the variation in attenuation due to the relativehumidity. As an example, a tuning detection threshold may be increased(e.g. made more stringent), responsive to an indication of a lowerrelative humidity (e.g. 20%), whereas the tuning detection threshold maybe decreased (e.g. made less stringent), responsive to an indication ofhigher relative humidity (e.g. 90%). Such examples are meant to beillustrative and are not meant to be limiting. Furthermore, the tuningdetection thresholds may be set based on a frequency or frequency(s)selected for detecting objects. More specifically, the tuning detectionthresholds may vary as a function of the frequency or frequency(s)selected for detecting objects, and such tuning detection thresholds asa function of frequency may be stored in a lookup table at thecontroller, for example.

Returning to 915, if conditions are not indicated to be met for usingeither intake oxygen sensors, or exhaust oxygen sensors, in order todetermine ambient humidity, then method 900 may proceed to 930. At 930,method 900 may include determining humidity via one or more ultrasonicsensor(s), as discussed in detail above with regard to FIGS. 4-7. As themethodology for determining humidity via ultrasonic sensors has beenpreviously discussed, for the sake of brevity, the methodology will notbe reiterated here. However, it may be understood that any aspects ofthe methods depicted in FIGS. 4-7 may be utilized in order to determineambient humidity via the use of ultrasonic sensor(s).

As an example, in some cases, one or more camera(s) may be used in orderto identify suitable objects for humidity measurements via an ultrasonicsensor, as described above with regard to FIG. 7. However, there may becases where a vehicle may not be equipped with a camera. In such anexample case, one or more ultrasonic sensors may be systematicallytested using the methods described above with regard to FIGS. 4-6, inorder to determine ambient humidity. In other words, detecting thepresence of an object may be conducted from one or both of: theultrasonic sensor positioned on the vehicle, and one or more onboardcameras. While not explicitly shown in FIG. 9, it may be understood thatif conditions are not met for using intake or exhaust oxygen sensors fordetermining ambient humidity at step 915, and if subsequent attempts todetermine ambient humidity via ultrasonic sensor(s) are not successful(e.g. suitable objects not identified via cameras and/or ultrasonicsensors), then method 900 may be delayed until appropriate conditionsare indicated for determining ambient humidity.

Proceeding to step 925, method 900 may include adjusting vehicleoperating parameters based on the recent humidity measurement, asdetermined via the ultrasonic sensor(s). As an extensive description ofstep 925 is described above, for the sake of brevity the multitude ofpotential adjustments to vehicle operating parameters as a function of adetermined humidity change will not be reiterated here. However, it maybe understood that any and all of the vehicle operating parametersadjusted responsive to a humidity determination via intake or exhaustoxygen sensor(s) may additionally be adjusted responsive to humiditydetermination via one or more ultrasonic sensor(s).

In this way, changes in ambient conditions (e.g., temperature, pressure,etc.) that influence humidity, may be used to trigger humiditymeasurement, where the humidity measurement may be conducted responsiveto vehicle operating conditions such that a likelihood of obtaining anaccurate indication of ambient humidity is increased. In other words, bydetermining vehicle operating conditions responsive to a request for ahumidity measurement, an appropriate method of determining humidity maybe indicated and carried out according to method 900 depicted in FIG. 9.

In another example, an ultrasonic sensor may be used to adjust vehicleoperating conditions, where a knowledge of percent relative humidity mayfurther be advantageous to the adjusting of the vehicle operatingconditions. In such an example, ultrasonic sensor(s) may additionally beemployed to determine humidity, where vehicle operations are furtheradjusted based on the humidity measurement. More specifically, abyproduct of diesel fuel combustion is carbon particles, referred to assoot. Emissions control devices, such as diesel particulate filters(DPF) (e.g. 72) reduce soot emissions from an engine by trapping sootparticles. Regeneration of the filter may be intermittently conducted,as the filter becomes saturated with soot. For example, the temperatureof the filter may be raised to a predetermined level to oxidize or burnthe accumulated particulate matter. In some examples, regeneration maybe accomplished by injecting additional fuel into an exhaust stream. Inother examples, regeneration may be accomplished by altering operationof the engine, such that exhaust temperature is increased. In stillother examples, a heater (e.g. 75) may be utilized to selectively heatthe DPF. Filter regeneration may occur during normal driving conditions,or may be initiated at other times, such as when a vehicle is stopped,when commanded by a vehicle operator, during servicing of the vehicle,etc. As regeneration involves increasing exhaust temperature, it may beadvantageous to conduct such a procedure only if it is indicated that anobject is a particular distance from the exhaust.

However, a factor that may contribute to a desired distance of an objectfrom a vehicle exhaust during a DPF regeneration event may includepercent relative humidity. For example, heat transfer through air may bea function of ambient temperature and humidity. Thus, if both ambienttemperature and humidity are known, thresholds for a distance between anobject and an exhaust may be adjusted accordingly, for a particular DPFregeneration event, as will be discussed in greater detail below.

Turning now to FIG. 10, a graph 1000 illustrating a relationship betweentemperature, humidity, and thermal conductivity of air (in watts permeter kelvin), is shown. More specifically, an x-axis depicts airtemperature ranging from 0° C. to 100° C., and a y-axis depictingthermal conductivity of air ranging from 0.024 W/m*K to 0.033 W/m*K, isshown. Furthermore, various plots illustrating percent humidity areshown. More specifically, plot 1005 illustrates 0% humidity, plot 1010illustrates 10% humidity, plot 1015 illustrates 20% humidity, plot 1020illustrates 30% humidity, plot 1025 illustrates 40% humidity, plot 1030illustrates 50% humidity, plot 1035 illustrates 60% humidity, plot 1040illustrates 70% humidity, plot 1045 illustrates 80% humidity, plot 1050illustrates 90% humidity, and plot 1055 illustrates 100% humidity. Asillustrated, thermal conductivity of air is a function of temperatureand humidity. For example, thermal conductivity of air at 100% humidityincreases from 0° C. to about 60° C. However, if the temperature isincreased further, thermal conductivity decreases. Thus, because thermalconductivity is a function of temperature and ambient humidity, if bothvariables (temperature and ambient humidity) are known, then thermalconductivity of air may be determined, and a threshold for a distancebetween an exhaust and an identified object may be adjusted accordingly,as will be described in detail according to the method depicted in FIG.11.

Turning now to FIG. 11, a high level example method for conducting a DPFregeneration procedure, is shown. More specifically, responsive toconditions being met for DPF regeneration, and where a vehicle speed isindicated to be below a threshold speed, objects in proximity to avehicle exhaust and their distance from the exhaust may be determined,and ambient humidity and ambient temperature indicated. Based on theindicated distance of objects in proximity to the exhaust, and furtherbased on the indicated ambient humidity and temperature, a distancethreshold may be adjusted such that, if an object is positioned at adistance from the exhaust less than the adjusted threshold distance,regeneration of the filter may be postponed until more favorableconditions for DPF regeneration are met. Said another way, the methoddepicted in FIG. 11 includes regenerating a particulate filter coupledto an underbody of the motor vehicle by causing burning of particulatestored in the particulate filter resulting in hot gases exiting a rearof the motor vehicle; selecting the selected sensor based on atransmission path of the selected sensor overlapping at least a portionof the hot gases exiting the rear of the motor vehicle; and postponingor aborting the regeneration based on there being an object within apredetermined distance of the hot gases exiting the rear of the motorvehicle. As one example the method may further include measuring an airtemperature near where the hot gases exit the rear of the motor vehicle;determining thermal conductivity of air based, at least in part, on theindication of relative humidity and the air temperature; and adjusting adistance threshold for the regeneration procedure, where the adjustingthe distance threshold includes decreasing the distance threshold asthermal conductivity decreases, and increasing the distance threshold asthermal conductivity increases.

Method 1100 will be described with reference to the systems describedherein and shown in FIG. 1, though it should be understood that similarmethods may be applied to other systems without departing from the scopeof this disclosure. Method 1100 may be carried out by a controller, suchas controller 12 in FIG. 1, and may be stored at the controller asexecutable instructions in non-transitory memory. Instructions forcarrying out method 1100 and the rest of the methods included herein maybe executed by the controller based on instructions stored on a memoryof the controller and in conjunction with signals received from sensorsof the engine system, such as the sensors described above with referenceto FIG. 1. The controller may employ vehicle system actuators such asultrasonic sensor(s) (e.g. 185), camera(s), a hydrocarbon (HC) reductantdelivery system (e.g. 74), fuel injector(s) (e.g. 66), DPF heater (e.g.75), etc., according to the method below.

Method 1100 begins at 1105 and may include determining current vehicleoperating conditions. Operating conditions may be estimated, measured,and/or inferred, and may include one or more vehicle conditions, such asvehicle speed, vehicle location, etc., various engine conditions, suchas engine status, engine load, engine speed, A/F ratio, etc., variousfuel system conditions, such as fuel level, fuel type, fuel temperature,etc., various evaporative emissions system conditions, such as fuelvapor canister load, fuel tank pressure, etc.

Proceeding to 1110, method 1100 may include determining a loading stateof a diesel particulate filter (DPF) (e.g. 72). Various strategies maybe used to determine a loading state of the DPF in order to indicatewhether the DPF filter may need to be regenerated. For example, athreshold pressure difference across the DPF may be indicative of aloading state of the DPF above a threshold loading state. In such anexample, one pressure sensor (e.g. 80) may be positioned upstream of theDPF, and another pressure sensor (e.g. 82) may be positioned downstreamof the DPF, such that a pressure differential across the DPF may becommunicated to the vehicle controller. In other examples, loading stateof the DPF may be inferred or estimated as a function of a number ofmiles the vehicle has been driven since a previous DPF regenerationprocedure. In a still further example, loading state of the DPF may beinferred or estimated as a function of a duration of engine operationsince a previous DPF regeneration procedure. Such examples are meant tobe illustrative and in no way limiting. For example, other methods ofindicating DPF loading state known in the art may be utilized, withoutdeparting from the scope of this disclosure.

Proceeding to 1115, it may be indicated whether conditions are met forconducting a DPF regeneration procedure. For example, if a DPF loadingstate is indicated to be above the predetermined threshold, as discussedabove with regard to step 1110 of method 1100, then it may be indicatedthat DPF regeneration conditions are met. However, if DPF regenerationconditions are not met, method 1100 may proceed to 1120. At 1120, method1100 may include maintaining current vehicle operating parameters. Forexample, at 1120, method 1100 may include continuingnon-DPF-regeneration engine operation, and the DPF may continue tocollect soot and monitor the DPF loading state.

Returning to 1115, if regeneration conditions are indicated to be met,method 1100 may proceed to 1125, and may include indicating whether thevehicle is traveling above a predetermined velocity threshold. Forexample, the predetermined velocity threshold may be a predeterminedthreshold velocity at which convection from external environmental airmay be sufficient to reduce exhaust gas outlet temperatures below athreshold temperature. In such an example, potential issues with objectsbeing positioned close to the exhaust may be disregarded, as exhausttemperatures are not likely to pose a significant issue due to thereduction in exhaust gas outlet temperatures due to air flow.Furthermore, as the vehicle is traveling at a velocity greater than thepredetermined velocity threshold, likelihood of an object beingpositioned close to the exhaust may additionally be low so as not topose a significant concern. Accordingly, if at 1125 it is indicated thatthe vehicle is traveling above the predetermined velocity threshold,method 1100 may proceed to 1130, and may include conducting theregeneration procedure without determining whether an object is within apredetermined distance of the hot gases exiting the rear of the motorvehicle.

Regenerating the DPF at 1130 may include adjusting engine operatingparameters such that the DPF may be regenerated. For example, the enginecontroller may include stored instructions for regenerating the DPF.Examples may include operating a heater (e.g. 75) coupled to the DPF, orby raising a temperature of engine exhaust (e.g. by operating rich, ordirect injection of fuel into exhaust gas), where the raised engineexhaust gas may serve to raise DPF temperature to convert soot in theDPF to ash.

Regeneration of the DPF at 1130 may further include determining whethersoot load is lower than a predetermined threshold. For example, thepredetermined threshold may include a lower threshold below whichregeneration of the DPF may be terminated. Regeneration may bemaintained, until soot load is lower than the predetermined threshold,for example. In such an example, a loading state of the DPF may beindicated via, for example, a pressure differential across the DPF.However, as discussed above, other methods of indicating DPF loadingstate may be utilized without departing from the scope of thisdisclosure.

If the DPF load is sufficiently low (e.g. below the predeterminedthreshold), then regeneration of the DPF may be terminated. Terminationmay include discontinuing any vehicle operating parameter contributingto the heating of the filter. For example, if fuel was being injectedinto the exhaust gas, such injection may be terminated. In anotherexample, if fuel injection to the engine was commanded rich, such fuelinjection may similarly be discontinued and fuel injection returned todefault operation, where default operation may include an operationalstate prior to conducting the DPF regeneration procedure. In still otherexamples, if a heater was activated in order to regenerate the DPF, thenthe heater may be deactivated. In all such examples, the actions may becontrolled by a vehicle controller (e.g. 12), where by signals are sentto the various actuators (e.g. fuel injectors, heater) to terminate theregeneration operation.

Continuing at 1135, method 1100 may include updating vehicle operatingconditions. For example, a loading state of the DPF may be updated basedon the recent DPF regeneration procedure. Such updated information maybe stored at the controller, for example. Furthermore, based on theregeneration procedure and subsequent DPF loading state, a regenerationschedule stored at the controller may be updated. For example, in a casewhere a regeneration schedule includes requesting a regenerationprocedure after a predetermined number of miles driven, or after apredetermined number of hours of engine operation, such numbers may bereset at the controller in order to effectively request a futureregeneration procedure. Method 1100 may then end.

Returning to 1125, if the vehicle is not indicated to be traveling abovethe predetermined threshold speed, then method 1100 may proceed to 1140.At 1140, method 1100 may include detecting objects in proximity to thevehicle exhaust, and may further include determining relative humidity,if possible. For example, if the vehicle is equipped with one or morerear-facing cameras, such camera(s) may be commanded by the controllerto search an area at the rear of the vehicle. Such an examplemethodology for utilizing available onboard camera(s) in order to detectobjects, and where, responsive to detection of suitable object, relativehumidity may be determined, is depicted above in the methods illustratedin FIGS. 7, and 4-6. In a case where determining humidity is possible,it may be understood that ambient temperature may additionally bedetermined, as discussed above with regard to FIGS. 4-6. Furthermore, itmay be understood that an ultrasonic sensor may be selected fordetermining relative humidity, where the ultrasonic sensor is selectedfrom a plurality of sensors based on the selected sensor transmissionand receipt path overlapping at least a portion of the hot gases exitingthe rear of the motor vehicle.

Exhaustive description of how one or more camera(s) may be utilized todetect objects that may be in a position close to the exhaust will notbe reiterated here, as it has been discussed above. Briefly, the one ormore camera(s) may be commanded by the controller to search for objectsat the rear of the vehicle that may be in close proximity to theexhaust. If such objects are detected, it may be further indicated, asdiscussed above, as to whether the objects appear to be stationary withrespect to the vehicle, whether the vehicle is moving or is parked. Forexample, multiple camera images may be obtained, where if objects areindicated to change position, size, or shape, between images, then itmay be determined that such an identified object may not be stationarywith respect to the vehicle. In some examples, ultrasonic sensors mayadditionally or alternatively be used to identify objects, and toindicate whether the identified objects appear to be stationary withrespect to the vehicle.

If, based on the one or more rear-facing camera(s) (or ultrasonicsensors), potential objects are indicated that may be stationary withrespect to the vehicle (e.g. moving car traveling at the same speed anddirection as the vehicle attempting to conduct a DPF regenerationprocedure), humidity may further be determined, according to the methodsdescribed above in FIGS. 4-6. As discussed above, it may be understoodthat the ultrasonic sensor may be selected for use in conducting ahumidity determination based on the ultrasonic signals overlapping atleast a portion of the hot gases exiting the rear of the vehicle.Furthermore, in determining ambient temperature, a temperature sensormay be selected that is in close proximity to the vehicle exhaust.

Some examples may include a vehicle that is not traveling, but rather isstationary (e.g. parked). In some examples, parked regeneration mayinclude a vehicle operator putting a vehicle transmission (not shown) inneutral, applying a parking break (not shown), pressing and releasing aclutch pedal (not shown), and pressing and holding a regeneration buttonon a vehicle dashboard until RPMs increase, and wherein the DPFregeneration procedure may commence. In such an example, when theregeneration is complete, lights on the dashboard may go out, indicatingcompletion of the regeneration event. While the vehicle is parked, itmay be likely that the one or more rear-facing camera(s) and/orultrasonic sensors may detect one or more objects in a proximity to theexhaust, and where an accurate measurement of humidity may be obtained,as discussed above and according to the methods depicted above withregard to FIGS. 4-6.

As discussed above, because humidity may have an effect on operationaluse of an ultrasonic sensor, by determining relative humidity, it may bepossible to adjust (correct) a distance detection threshold for theultrasonic sensor being used to determine distance between the vehicleand an object of interest. For example, because certain frequencies maybe differentially attenuated as a function of relative humidity, adistance detection threshold for individual frequencies based on thedetermined relative humidity may be indicated, and stored in a lookuptable at the controller (e.g. 12). For example, at high humidityindications, frequencies in a lower range (20-40 kHz) may be utilized,instead of higher frequencies, such that operational use of theultrasonic sensor may be improved.

Furthermore, in attempting to detect objects in proximity to the vehicleexhaust, only those one or more ultrasonic sensors configured on thevehicle for detecting objects to the rear of the vehicle may be employedfor determining relative humidity and detecting objects at 1140.

In some examples, a vehicle may not be equipped with one or morerear-facing camera(s). In such an example, one or more ultrasonicsensors positioned at the rear of the vehicle may be commanded toconduct a relative humidity estimate, and a distance measurement,according to the methods described above and illustrated in FIGS. 4-6.For example, ultrasonic sensors may be used in lieu of cameras to detectobjects in proximity to the exhaust. Ultrasonic sensors may further beused to detect objects that appear stationary with respect to thevehicle (e.g. indicated via the same transit time between two or moreultrasonic frequencies), such that a humidity measurement may beobtained, and an accurate distance measurement may thus be conducted.

Proceeding to 1145, if no objects were detected, method 1100 may proceedto 1130, and may include regenerating the DPF, as described in detailabove. However, if objects were detected and, where possible, if anestimate of humidity was determined, then method 1100 may proceed to1150.

As discussed above, thermal conductivity of air may be a function of airtemperature and relative humidity. Accordingly, responsive to objectsbeing detected and a humidity measurement being conducted, method 1100may include measuring ambient temperature at 1150. As discussed above,measuring ambient temperature may be conducted via an outside airtemperature (OAT) sensor (e.g. 127). Such an indication of outside airtemperature may be stored at the controller (e.g. 12), for example. Withan object detected, and with relative humidity (where possible) andambient air temperature determined, method 1100 may proceed to 1155. At1155, method 1100 may include adjusting a distance threshold based onthe relative humidity measurement and ambient temperature determination,where air temperature is measured near where hot gases exit the rear ofthe motor vehicle. For example, the distance threshold may comprise adistance that, above which a DPF regeneration procedure may be conductedwithout concern that heat from the exhaust may adversely impact thedetected object (or objects). In a case where humidity was not able tobe determined, rather than adjusting the distance threshold, apredetermined distance threshold may instead be utilized.

More specifically, as illustrated in FIG. 10, thermal conductivity ofair may fluctuate as a function of humidity, and temperature. As anexample, at 60° C. and 80% humidity (e.g. line 1045), thermalconductivity of air may be ˜0.0275 W/m*K, whereas at 90° C. and 80%humidity, thermal conductivity of air may be ˜0.026. In other words,thermal conductivity may decrease as temperature increases from 60° C.to 90° C. when ambient humidity is at 80%. Thus, heat may not beconducted as efficiently in air as temperature increases from 60° C. to90° C. under conditions where ambient humidity is 80%. Accordingly,method 1100 may include adjusting the distance threshold for theregeneration procedure, where the adjusting the distance thresholdincludes decreasing the distance threshold as thermal conductivitydecreases, and increasing the distance threshold as thermal conductivityincreases.

Such conditions are meant to be illustrative, but it may be understoodthat the distance threshold may be adjusted accordingly based on anyrelative humidity measurement and temperature measurement, according tothe graph 1000 depicted in FIG. 10. In one example, a lookup table maybe stored at the controller, where the lookup table may include anamount whereby the distance threshold may be adjusted based on indicatedrelative humidity and temperature. As such, for any given pair ofrelative humidity and temperature measurements, an amount whereby thedistance threshold may be adjusted may be readily obtained. Importantly,by using the ultrasonic sensor to detect both ambient humidity anddistance between the sensor and the indicated object, accuracy of theadjusting of the distance threshold may be increased, as compared to acondition where ambient humidity may be inferred from another means(e.g. intake or exhaust oxygen sensors). More specifically, becausehumidity may be localized, obtaining humidity via the use of ultrasonicsensors just prior to adjusting the distance threshold may beadvantageous in that humidity may be accurately determined specificallyfor the purpose of adjusting the distance threshold. Furthermore,because the ultrasonic sensor for determining humidity may be selectedbased on at least a portion of the transmission and receipt path of theultrasonic sensor overlapping the hot gases exiting the rear of themotor vehicle, humidity determination results may specifically reflecthumidity conditions near the rear of the vehicle where hot gases areexpected during the DPF regeneration procedure.

After adjusting the distance threshold as a function of determinedambient humidity and temperature at 1155, method 1100 may proceed to1160. At 1160, method 1100 may include indicating whether distancebetween the object of interest and the exhaust is greater than, or lessthan, the adjusted distance threshold. For example, the ultrasonicsensors may be utilized to determine a distance of the indicated objectfrom the exhaust. If the object is indicated to be positioned less thanthe adjusted distance threshold away from the exhaust, method 1100 mayinclude returning to step 1125, and may include continuing to determinewhether conditions are present for conducting the DPF regenerationprocedure. However, if the object is indicated to be positioned greaterthan the adjusted distance threshold away from the exhaust, method 1100may proceed to 1130, and may include regenerating the DPF filter, asdescribed in detail above.

While not explicitly illustrated in FIG. 11, it may be understood thatwhile the DPF is being regenerated, one or more of the onboard camera(s)and ultrasonic sensor(s) may be utilized in order to ensure that anobject does not cross the adjusted distance threshold while the DPFregeneration is taking place. For example, the one or more camera(s) maybe commanded by the controller to record images over the course of theDPF regeneration event, and process the images as discussed above usingobject recognition algorithms stored at the controller, such that it maybe indicated whether any objects appear to have moved during theregeneration event, and importantly, whether the objects appear to havemoved to a position that may be less than the adjusted distancethreshold away from the vehicle exhaust. Such examples may includedetermining the distance between the exhaust and the identified objects,via the ultrasonic sensor(s), for example. In a case where one or morecameras may not be included in the vehicle, then the ultrasonicsensor(s) may be utilized solely to determine distance of the identifiedobject(s) from the vehicle exhaust. In an example case where it isdetermined that an object or objects are positioned below the adjusteddistance threshold, then the regeneration event may be abruptlyterminated, or suspended. Such an action may be carried out by thecontroller, for example. By monitoring the DPF regeneration event viathe use of one or more camera(s) and ultrasonic sensor(s), the presenceof an object at a position less than the adjusted distance threshold maybe readily identified, such that the DPF regeneration event may besuspended. Said another way, method 1100 may include conducting theregeneration procedure responsive to the object being positioned at agreater distance than the threshold distance; monitoring the object andan area proximate the rear of the vehicle via the one or more camerasduring the regeneration procedure; and terminating the regenerationprocedure if the object or other object is identified as being closerthan the threshold distance during the regeneration procedure.

As discussed above, by indicating ambient temperature and ambienthumidity, two noise factors for ultrasonic sensors, a distance detectionthreshold may be adjusted such that operational use of the ultrasonicsensor may be improved. However, it may be further desirable to selectoptimal frequencies for particular distance measurements, provided thereis an indication of whether an object of interest may be a shortdistance (short range) away, a medium distance (medium range) away, or along distance (long range) away from the ultrasonic sensor. By using anoptimal frequency for a particular distance measurement, where adistance detection threshold has been adjusted, operational use of theultrasonic sensor may be still further improved. In some examples, theoptimal frequency may be a function of the adjusted distance detectionthreshold, and the desired operational use of the sensor. In someexamples, a plurality of images of an environment proximal to thevehicle may be captured via one or more onboard cameras, where thedesired operational use of the sensor is at least partially determinedvia the one or more cameras, as will be discussed in further detailbelow.

Turning now to FIG. 12, a high level example method for adjusting adistance detection threshold for an ultrasonic sensor and furtherdetermining optimal frequency(s) for distance measurements, is shown.More specifically, by determining ambient humidity and ambienttemperature, two noise factors for ultrasonic distance measurements maybe controlled for, such that a distance detection threshold for theultrasonic distance measurement may be adjusted. As a function of theadjusted distance detection threshold, optimal frequency(s) for asubsequent distance determination may be selected. In some examples, thesame ultrasonic sensor used to conduct the humidity determination may besubsequently used to conduct a distance measurement. However, in otherexamples, the sensor used to determine relative humidity may be adifferent sensor.

Method 1200 will be described with reference to the systems describedherein and shown in FIG. 1, though it should be understood that similarmethods may be applied to other systems without departing from the scopeof this disclosure. Method 1200 may be carried out by a controller, suchas controller 12 in FIG. 1, and may be stored at the controller asexecutable instructions in non-transitory memory. Instructions forcarrying out method 1200 and the rest of the methods included herein maybe executed by the controller based on instructions stored on a memoryof the controller and in conjunction with signals received from sensorsof the engine system, such as the sensors described above with referenceto FIG. 1. The controller may employ fuel system and evaporativeemissions system actuators, such as ultrasonic sensor(s) (e.g. 185),camera(s) (e.g. 186), etc., according to the method depicted below.

Method 1200 begins at 1205 and may include indicating whether an objectof interest has been detected. As discussed above with regard to FIG. 7,detecting and indicating objects of interest may in some examples beconducted via one or more onboard camera(s). As a procedure fordetecting objects via one or more camera(s) has been thoroughlydiscussed above, for brevity, a full description will not be reiteratedhere. However, it may be understood that at 1205, object detection andindication of suitable objects may be determined via one or morecamera(s) as discussed above at FIG. 7. In some examples, a vehicle maynot be equipped with one or more camera(s), or the vehicle may beequipped with camera(s) but not necessarily in optimal position fordetecting all potential objects positioned around the vehicle. In suchan example, one or more ultrasonic sensor(s) may additionally oralternatively be utilized in order to detect and indicate potentialsuitable objects of interest. In some examples, an object search may beinitiated based on humidity determination conditions being met, such asan indicated change in ambient temperature or pressure, described aboveat step 905 of method 900. In another example, suitable objects may bedetected while a vehicle is performing an assisted, or fully automated,parking procedure. Such examples and meant to be illustrative, and arenot meant to be limiting.

If, at 1205, no suitable objects of interest are indicated, method 1200may proceed to 1210 and may include maintaining current vehicleoperating parameters. For example, if the controller was commanded tosearch for suitable objects of interest via camera(s) and/or ultrasonicsensor(s), then at 1205, method 1200 may continue searching for thesuitable objects of interest.

Alternatively, if at 1205 method 1200 indicates that a suitable objectof interest may be identified, method 1200 may proceed to 1215. At 1215,method 1200 may include determining humidity, via the use of anultrasonic sensor, as described above. More specifically, determininghumidity may include determining ambient temperature at 1220, via, forexample, an OAT sensor (e.g. 127). Furthermore, determining ambienthumidity may additionally include performing the variable frequencyalgorithm (FIG. 5) and delta attenuation calculation (FIG. 6). In otherwords, determining ambient humidity at 1215 may comprise determininghumidity according to the high level method of FIG. 4. Because themethod for determining humidity via the use of an ultrasonic sensor hasbeen described in detail above, for brevity an in-depth explanation willnot be reiterated here. However, it may be understood that determiningambient humidity at 1215 may be accomplished via following the methoddepicted in FIG. 4.

Responsive to humidity (and ambient temperature) being determined,method 1200 may proceed to 1230. At 1230, method 1200 may includeadjusting a distance detection threshold for the ultrasonic sensor thatwas utilized to make the humidity determination. For example, a maximumrange at which an ultrasonic sensor can detect a target object may beaffected by attenuation of sound, where a major noise factor in terms ofsound attenuation may comprise ambient humidity. Furthermore, anaccurate determination of the speed of sound may be important forconverting a transit time from sending to receipt of an ultrasonicsignal into a distance measurement. As the speed of sound is influencedby ambient temperature, knowledge of the ambient temperature may furtherincrease operational use of the ultrasonic sensor. Furthermore, accurateestimation of ambient humidity may necessitate a knowledge of ambienttemperature, as discussed above. Accordingly, at 1230, adjusting thedistance detection threshold may be based on the indicated humidity andambient temperature. In some examples, the distance detection thresholdmay be frequency dependent, such that the distance detection thresholdmay be different for different frequencies. As an example, a distancemeasurement greater than a particular distance may not be achievable at100 kHz, at a relative humidity percentage of 80%, but may be achievableinstead via the use of 30 kHz, due to a reduction in attenuation ofsound at 30 kHz as compared to 100 kHz at 80% humidity. Such an exampleis meant to be illustrative. Accordingly, responsive to determination ofhumidity, distance detection threshold(s) at various frequencies, forthe indicated humidity, may be determined and stored in a lookup table,for example. Said another way, in some examples, adjusting the distancedetection threshold for the ultrasonic sensor responsive to anindication of relative humidity may include indicating suitablefrequencies for conducting distance measurements, as a function of theindication of relative humidity.

Proceeding to 1235, method 1200 may include determining desiredoperational use of the ultrasonic sensor, such that the sensor may beused to conduct a distance measurement based on the desired operationaluse of the sensor. More specifically, determining desired operationaluse may comprise determining whether a particular object for which adistance determination is desired is located at a short range (e.g. lessthan 1 meter), at a medium range (e.g. greater than one meter but lessthan 2 meters), or at a long range (e.g. greater than 2 meters). In oneexample, determining a range for which a particular object is positionedaway from the ultrasonic sensor may include estimating a distance(range) via the use of the one or more onboard camera(s), if equipped.For example, via the use of object recognition software commonly knownin the art, algorithms for which may be stored at the controller, arough distance estimation may be obtained simply via the use of theonboard cameras. In another example, a rough calculation may beindicated by initial ultrasonic sensor distance determination. In suchan example, because the distance to the object is not known, one or moreparticular frequency(s) may be sent and received by the ultrasonicsensor in order to make a rough distance determination calculation. Sucha calculation may include determining whether the distance between theultrasonic sensor and the object of interest is a short range, mediumrange, or long range, away from the sensor.

Accordingly, at 1235, determining desired operational use of ultrasonicsensors may include retrieving information from a lookup table stored atthe controller, for example the lookup table depicted in FIG. 13.

Turning to FIG. 13, an example lookup table is depicted, illustrating anoptimal ultrasonic frequency that may be used for distance measurements,responsive to the object of interest being indicated to be positioned ata short range, medium range, or long range away from the ultrasonicsensor used for conducting the distance measurement. As will bediscussed below, the desired frequency(s) to use may be further selectedas a function of the adjusted distance detection thresholds, describedabove.

As one example, if the desired distance of an object of interest isindicated to be positioned at a short range away from the ultrasonicsensor, then all frequencies that the ultrasonic sensor is capable oftransmitting (e.g. 20 kHz to 100 kHz), may in theory be utilized for adistance measurement, as sound attenuation may not play a large role atshort range. However, based on the distance detection threshold, somefrequencies may still be desired over others. In any case, for shortrange distance measurements, because most if not all frequencies mayprovide accurate distance measurements due to little effect of soundattenuation, the frequency that may be chosen may comprise an optimalfrequency that the piezoelectric crystal of the ultrasonic sensor wasdesigned to operate at. For example, this frequency may be a knownvalue, and may be stored at the controller. If, based on the adjusteddistance detection threshold, such a frequency is not desirable due topotential attenuation at such a frequency, then a lower frequency may beselected, for example.

As another example, if the desired distance of an object of interest isindicated to be positioned at a medium range away from the ultrasonicsensor, then frequencies in a low to middle range (e.g. 20 kHz to 50-60kHz) may be selected to conduct the distance measurement for increasedaccuracy. In such an example, if the adjusted distance detectionthreshold excludes any of the potential frequencies from being used,then frequencies other than those excluded frequencies may be selected.For example, at 60 kHz, sound attenuation due to a particular relativehumidity may result in objects not being able to be accurately detected(e.g. distance measurement not accurate) at 1.5 meters away from anultrasonic sensor, but other lower frequencies may enable accuratedetection and measurement. Such an indication may be provided via theadjusted distance detection lookup table, described above with regard tostep 1230 of method 1200. In any case, whether certain frequencies inthe low to middle range may be excluded based on the adjusted distancedetection threshold or not, a frequency may be chosen such that thefrequency chosen is within the range for optimal accuracy, and which isclosest to the optimal frequency that the sensor was designed to operateat. As discussed above, such an indication of optimal frequency may bestored at the controller.

As a still further example, if the desired distance of an object ofinterest is indicated to be positioned at a long range away from theultrasonic sensor, then low frequency operation (e.g. between 40 kHz and20 kHz) may be selected to conduct the distance measurement forincreased accuracy. As discussed above, if the adjusted distancedetection threshold excludes any of the potential frequencies from beingused, then frequencies other than those excluded may be selected.Similar to that described above for the medium range, whether certainfrequencies are excluded or not, a frequency may be chosen such that thefrequency chosen is within the range for desired operation, and which isclosest to the optimal frequency that the sensor was designed to operateat.

Returning to 1235, responsive to determining desired operational use ofthe ultrasonic sensor, method 1200 may proceed to 1240. At 1240, method1200 may include conducting the distance measurement, or measurements,via sending and receiving the ultrasonic wave frequency chosen as anoptimal frequency at step 1235. As discussed above, the controller maycommand an oscillating voltage to be sent to the ultrasonic sensor, thusconverting electrical oscillation into mechanical sound waves that maybe transmitted from the ultrasonic sensor. After being reflected fromthe object of interest, the sound waves may be received by the sensor(e.g. receiver), where receiving the sound waves involves converting themechanical waves back to electrical oscillations that may be interpretedby the controller. Based on the transit time from transmission toreceipt of the reflected waves, a distance measurement may be indicated.More specifically, as discussed above, distance may be indicated basedon the formula d=c*t/2 where c is the speed of sound and t is thetransit time.

Furthermore, at 1240, tuning detection thresholds may additionally beadjusted responsive to the indication of humidity. As discussed above,adjusting tuning detection thresholds may comprise adjusting a voltagelevel for indication of an object, as compared to noise, via the one ormore ultrasonic sensor(s). The tuning detection thresholds may vary as afunction of the frequency or frequency(s) selected for detectingobjects, and such tuning detection thresholds as a function of frequencymay be stored in a lookup table at the controller, for example.

In some examples, there may be instances where the chosen (selected)frequency for conducting the distance measurement results in asignal-to-noise issue, for one reason or another. For example, an angleof the object of interest may have changed, or the object may have movedfrom one distance to another, etc. Accordingly, proceeding to 1245,method 1200 may include indicating whether additional accuracy may bedesired. If attenuation or some other environmental effect resulted in asignal-to-noise issue during conducting the distance measurement, suchthat a desired distance estimate may not be obtained, then method 1200may proceed to 1250. At 1250, method 1200 may include actions such asvarying the ultrasonic frequency in an attempt to obtain improveddistance measurements between the ultrasonic sensor and the object ofinterest. For example, if a specific frequency was selected based on theobject being a middle range distance away from the sensor, then otherfrequencies corresponding to optimal middle range distance determinationmay be next utilized. In some examples, one or more camera(s) (if thevehicle is equipped) may be utilized in order to indicate whether theobject of interest may have moved (e.g. moved away or moved closer to orfurther from the ultrasonic sensor). In still other examples,frequencies outside of the chosen range may be utilized, in an attemptto increase the accuracy of the distance measurement. For example, ifthe object of interest was predicted to be at a middle range distance,and thus a frequency of 50 kHz was selected, then if a good distanceestimate was not obtained, a lower frequency (e.g. 30 kHz) may next beutilized, in an attempt to reduce attenuation. Such examples areillustrative and are not meant to be limiting.

Returning to 1245, if additional accuracy is not desired, in otherwords, if signal-to-noise of the transmitted and received ultrasonicsound wave is above a level where desired distance measurement(s) may beobtained, then method 1200 may continue to 1255, and may includeindicating the distance of the object. Such a distance determination maybe at least temporarily stored at the controller, in one example.Furthermore, in some examples, such distance determination methodologymay be utilized in order to more effectively carry out an assisted orfully automated parking maneuver, such as according to the systemdescribed above with regard to FIG. 2.

Turning now to FIG. 14, an example timeline 1400 depicting conducting anopportunistic humidity determination procedure, using the methodsdepicted in FIGS. 4-7, and FIG. 9 is shown. Timeline 1400 includes plot1405, indicating whether humidity determination conditions are met, overtime. Timeline 1400 further includes plot 1410, indicating whether avehicle engine is on, or off, over time. Timeline 1400 further includesplot 1415, indicating whether an object detection procedure has beeninitiated, over time. Timeline 1400 further includes plot 1420,indicating whether humidity has been determined, over time. Timeline1400 further includes plot 1425, indicating an amount of exhaust gasrecirculation (EGR) being provided to engine intake, over time. Timeline1400 further includes plot 1430, indicating relative humidity, overtime.

At time t0, the vehicle is in operation, being propelled via an engine,illustrated by plot 1410. Furthermore, humidity determination conditionsare not indicated to be met at time t0. As discussed above, conditionsfor a humidity determination procedure being met may include anindication of an ambient temperature change greater than a temperaturethreshold and/or a change in ambient pressure greater than a pressurethreshold since previous (e.g. last, or immediately preceding) humiditydetermination. Further conditions for a humidity determination procedurebeing met may include a threshold time of engine operation, or distanceof vehicle travel greater than a threshold distance since a lasthumidity measurement, or a change in weather conditions indicated byother means, such as via GPS and cross-referenced to the internet, etc.

As the vehicle is in operation and the humidity determination conditionshave not been indicated to be met at time t0, in this exampleillustration object detection via, for example, camera(s) and/orultrasonic sensor(s) is not indicated to be initiated. However, theremay be some circumstances where humidity determination conditions arenot met, yet object detection may still be initiated. Such examples mayinclude a vehicle conducting a parking event, where camera(s) and/oronboard ultrasonic sensor(s) may be employed to assist the parkingoperation, for example.

Furthermore, humidity is not indicated to have been determined since aprevious humidity measurement, indicated by plot 1420. As such, it maybe understood that “no” with regard to plot 1420 may refer to asituation where humidity has not been determined since a previoushumidity measurement, and wherein a current humidity measurement beingdetermined may be indicated by “yes” with regard to plot 1420.

Finally, at time t0, a determined amount of exhaust gas is beingrecirculated to the intake of the vehicle engine, where an amount of EGRmay be at least partially determined by a last, or previous humiditymeasurement. With regard to plot 1425, “+” may refer to increasingamounts of EGR, while “−” may refer to decreasing amounts of EGR.Furthermore, N/A may refer to a condition where no EGR is beingrecirculated to the engine intake, such as when the engine is notoperating, for example.

At time t1, humidity conditions are indicated to be met. Accordingly, itmay be determined whether conditions are met for determination ofhumidity via use of an exhaust gas oxygen sensor (e.g. UEGO), or otheroxygen sensor, where such an estimate may be determined via alternatingbetween applying first and second voltages to the exhaust gas sensor,and generating an indication of humidity based on sensor outputs at thefirst and second voltages, described above with regard to FIG. 8.However, because the engine is indicated to be in operation at time t1,conditions are not indicated to be met for determining humidity via theexhaust gas oxygen sensor. Instead, a humidity determination may beconducted via an ultrasonic sensor, provided a suitable object may beidentified such that an accurate measurement of humidity may beobtained.

Accordingly, proceeding to time t2, object detection may be initiated.For example, object detection may include the use of one or more vehiclecamera(s) (e.g. 186) in order to identify suitable objects forsubsequently determining humidity. In other examples, if the vehicle isnot equipped with one or more camera(s), then as an alternative theultrasonic sensor(s) themselves may be used to identify potentialsuitable objects for conducting a humidity measurement.

As discussed above, object detection may include the one or morecamera(s) capturing images, and storing the images at the controller(e.g. 12), for example. Such images may be processed via objectrecognition algorithms stored at the controller, in order to identifysuitable objects for conducting a humidity measurement. For example,suitable objects may include objects that are stationary with respect tothe vehicle, objects above a predetermined threshold size, objects witha predetermined shape, objects with an indicated lack of surfaceroughness, objects with a preferred angle of orientation, etc.

Between time t2 and time t3, it may be understood that, via the use ofone or more camera(s), a suitable object for conducting a humiditymeasurement is identified. Responsive to identification of a suitableobject, it may be further determined as to the objects position withrespect to the vehicle, such that an optimally positioned ultrasonicsensor may be utilized to conduct the humidity measurement. For example,as discussed above, camera sensor(s) (e.g. 187) may be used to indicatean approximate location of the object with respect to the vehicle, andthe controller may process the information in order to select anoptimally positioned ultrasonic sensor to utilize for the humiditymeasurement. More specifically, the selected ultrasonic sensor may beselected based on the object, identified by one of the cameras, beingwithin a transmission path of the selected sensor. As such, it may beunderstood that between time t2 and t3, a suitable object was detected,and an optimally positioned ultrasonic sensor was selected forconducting a humidity determination measurement. As the engine isoperating, and a suitable object was identified for conducting therelative humidity measurement, it may be understood that the suitableobject may likely be another vehicle traveling at essentially the samespeed and direction as the vehicle conducting the humidity measurement.As such, it may be understood that conducting a humidity measurement viaultrasonic sensors may be accomplished while the vehicle is in operation(e.g. being propelled via an engine or an onboard energy storagedevice).

Between time t2 and t3, after a suitable object has been identified, andan optimal ultrasonic sensor selected, a humidity measurement may beconducted. For the sake of brevity, the method of conducting thehumidity measurement will not be reiterated in full detail here.However, it may be understood that the humidity measurement may beconducted according to the methods depicted above with regard to FIGS.4-6. Briefly, determining humidity may comprise transmitting a pluralityof signals from a single sensor, each at a different frequency,receiving reflected signals of the transmitted signals, determiningattenuation values only for each of the reflected signals which have thesame transit time from transmission to receipt, determining differencesbetween pairs of the attenuation values, and converting the differencesto an indication of relative humidity.

Accordingly, at time t3, it is indicated that humidity has beendetermined. More specifically, humidity may be accurately determined tobe the value of humidity indicated by plot 1430 at time t3. Withhumidity determined, certain vehicle parameters may be adjustedaccordingly, as discussed in detail above with regard to FIG. 9. In thisexample illustrative timeline 1400, only one vehicle operating parameter(EGR) is illustrated, for clarity. As illustrated, because humidity isindicated to have increased, EGR may be reduced, in order to avoid leanengine operation due to the increase humidity. Accordingly, between timet3 and t4, EGR is reduced according to the latest humidity measurement.Furthermore, while not explicitly shown, it may be understood that themost recent humidity measurement may be stored at the controller. Stillfurther, while not explicitly illustrated, one or more additionalvehicle operating parameters may be adjusted responsive to the humiditymeasurement. For example, as discussed above, an amount of spark advanceor retard, a borderline spark value, a fuel octane estimate, etc., maybe adjusted.

At time t4, the vehicle engine is turned off. In this example timeline,the engine shutoff may be understood to include a deceleration fuelshutoff event (DFSO). However, while the engine is off, it may beunderstood that an intake and exhaust valve may be maintained activatedon at least one cylinder, such that the engine may cycle air through theintake manifold to the exhaust manifold. At time t5, humiditydetermination conditions are again met, indicated by plot 1405. Becausethe engine is off due to a DFSO event, an exhaust gas oxygen sensor(e.g. UEGO) may be utilized to determine humidity. In other words, suchan event may comprise an opportunity to preferentially conduct ahumidity measurement via the exhaust gas oxygen sensor over conducting ahumidity measurement via an ultrasonic sensor. A method for determininghumidity via the use of an exhaust gas oxygen sensor is detailed abovewith regard to the method depicted in FIG. 9. Thus, an in-depthdescription of how a humidity detection may be accomplished via anexhaust gas oxygen sensor will not be reiterated here. However, it maybe understood that, between time t5 and t6, a humidity determination(humidity indication) may be conducted via the exhaust gas oxygensensors. Accordingly, at time t6, it is indicated that a new ambienthumidity measurement has been determined, indicated by plot 1420. Assuch, the vehicle controller may update a previous humidity indicationwith the recent selected humidity indication.

The ambient humidity determination may be stored at the controller, suchthat vehicle operational parameters may be adjusted according to the newhumidity determination. As the engine remains off from time t6 to t7, noadjustments are made to the amount of EGR provided to the engine (e.g.none in this case as the engine is off). However, at time t7, the engineis again activated, and thus an amount of EGR provided to the engine isadjusted accordingly, based on the most recent humidity determinationmeasurement. In other words, the amount of EGR is adjusted based on thehumidity determined at time t6, and which was stored at the controller.

Between time t7 and t8, the vehicle operates via the engine, withvehicle parameters being adjusted according to the most recent humiditymeasurement conducted via the exhaust gas oxygen sensor while the enginewas deactivated (e.g. spun unfueled with at least one cylindermaintaining intake and exhaust valve function).

Turning now to FIG. 15, an example timeline 1500 is depictedillustrating how a distance threshold between an object of interest anda vehicle exhaust may be adjusted responsive to an indication of ambienthumidity. Timeline 1500 includes plot 1505, indicating whetherconditions are met for regeneration of a diesel particulate filter(DPF), over time. Timeline 1500 further includes plot 1510, indicating avehicle velocity, over time. Line 1511 represents a threshold velocity,above which a DPF regeneration may be conducted without taking intodetermining a position of a potential object with respect to an exhaustof the vehicle. However, below the threshold velocity, an object withina threshold distance of the exhaust may result in the DPF regenerationprocedure being aborted, or postponed.

Accordingly, timeline 1500 further includes plot 1515, indicatingwhether an object is detected as being positioned near the vehicleexhaust, over time. Timeline 1500 further includes plot 1520, indicatingwhether a humidity measurement has been obtained, over time, and whereit may be understood that “no” means that a humidity measurement has notbeen conducted since a previous humidity estimation, and where “yes”indicates a current humidity measurement has been conducted. Timeline1500 further includes plot 1525, indicating a position of an object withrespect to the vehicle exhaust, over time. In this example illustration“−” may refer to decreasing distance between an object and the vehicleexhaust, whereas “+” may refer to increasing distance between the objectand the vehicle exhaust. Line 1526 refers to a first distance threshold,and line 1527 refers to an adjusted, second threshold, where thethresholds may be adjusted based on an indication of ambient humidity,for example, discussed above and which will be discussed further below.Timeline 1500 further includes plot 1530, indicating whether DPFregeneration is taking place “yes”, or not “no”. Furthermore, timeline1500 further includes plot 1535, indicating humidity, and plot 1540,indicating ambient temperature, over time. For plot 1540, a “+”indicates increasing (e.g. higher) temperature, while a “−” indicatesdecreasing (e.g. lower) temperature.

At time t0, it may be understood that the vehicle is in operation, andtraveling at a low velocity, indicated by plot 1510. In some examples,such a low velocity may be indicative of a vehicle that is stopped, orsubstantially stopped. DPF regeneration conditions are not indicated tobe met, illustrated by plot 1505. Accordingly, a potential object ofinterest is not as of yet detected, illustrated by plot 1515, and thusobject position is not indicated. As DPF regeneration conditions are notmet, a DPF regeneration procedure is not in progress, illustrated byplot 1530. Actual humidity is near 100%, indicated by plot 1535, andfurthermore, a humidity determination procedure has not been conductedsince a last time a humidity determination procedure was conducted,illustrated by plot 1520.

At time t1, DPF regeneration conditions are indicated to be met,illustrated by plot 1505. As discussed above, DPF regenerationconditions may be met responsive to a threshold pressure differenceacross the DPF being reached, as indicated by one pressure sensor (e.g.80) positioned upstream of the DPF, and another pressure sensor (e.g.82) positioned downstream of the DPF. Other examples may include athreshold number of miles driven since a previous DPF regenerationprocedure, or a threshold duration of engine operation being reachedsince a previous DPF regeneration procedure.

Responsive to a DPF regeneration request, it may be determined whetherthe vehicle is traveling above a threshold velocity. The thresholdvelocity in this example timeline is illustrated by line 1511. If thevehicle is indicated to be traveling above the threshold velocity, thena DPF regeneration event may be conducted without first determiningwhether there is an object or objects close to the vehicle exhaust, asair flow due to the vehicle traveling velocity may serve to cool anddisperse exhaust gas such that objects near the exhaust do not pose aconcern. However, in this example timeline, the vehicle is indicated tobe traveling substantially below the threshold velocity. Accordingly,the controller may initiate a search for objects of interest positionedclose to the vehicle exhaust. As discussed above, such a search mayinclude the controller commanding one or more onboard camera(s) (e.g.186) to capture images in the proximity of the vehicle exhaust, andprocess the images using suitable object detection algorithms, in orderto indicate whether potential objects of interest are positioned closeto the exhaust. In other examples, if a vehicle is not equipped with oneor more camera(s), such a search may include using one or moreultrasonic sensor(s) (e.g. 185) to detect objects near the exhaust.

In this example timeline, it may be understood that at time t1, with DPFregeneration conditions being met, and the vehicle being indicated to bebelow the threshold velocity, one or more onboard camera(s) may becommanded via the controller to search for objects positioned near theexhaust. Accordingly, at time t2, potential objects are detected,indicated by plot 1515. Furthermore, during the search via the use ofone or more onboard camera(s), it may be understood that it wasdetermined that the potential object may be a suitable object forconducting an ambient humidity determination. Thus, a humiditydetermination procedure may be executed, as described in detail abovewith regard to FIGS. 4-6. As discussed above, conducting an ambienthumidity determination may additionally rely on a determination ofambient temperature. More specifically, in such an example where a DPFregeneration procedure may be conducted, it may be desirable to measureambient temperature as close as possible (e.g. near to) the vehicleexhaust, as temperature near the vehicle exhaust may be substantiallygreater than a temperature further away from the vehicle, due to engineoperation. Furthermore, such an increased temperature may affect alocalized humidity in a vicinity close to the vehicle exhaust, which maythus enable an adjustment of a distance threshold for enabling a DPFregeneration procedure. More specifically, an area of interest whenconducting a DPF regeneration procedure may encompass an area between avehicle exhaust and an object of interest, where that area mayexperience elevated temperatures which may thus affect a localizedhumidity in that area. Localized humidity differences may thus furtheraffect a thermal conductivity of the air in that specified area, asdiscussed above with regard to FIGS. 10-11, and therefore determiningtemperature and humidity specific to that area may enable adjustment ofa distance threshold for enabling a DPF regeneration procedure.

At time t3, it is indicated that a humidity determination procedure hasbeen completed and that an ambient humidity has been determined. Asdiscussed above and with regard to FIGS. 10-11, depending on percenthumidity, thermal conductivity of air may vary. As such, knowledge ofambient temperature may enable adjustment of a distance threshold forconducting, or not conducting, a DPF regeneration procedure. Accordinglyat time t3, a distance threshold may be adjusted. More specifically, adistance threshold may be set at a first threshold level, indicated byline 1526. In such an example, if an object is positioned closer to theexhaust than the threshold, then a DPF regeneration event may not beconducted (e.g. may be prevented from being conducted), and may bepostponed. However, if an object were positioned at a greater distancefrom the exhaust than the threshold, then a DPF regeneration proceduremay be conducted. In this example timeline, based on determined humidityand temperature, where the temperature may correspond to a temperaturesubstantially near the vicinity of the exhaust, and where humidity maycorrespond to a localized humidity in the vicinity of the exhaust (e.g.roughly between the exhaust and an object of interest), the distancethreshold may be adjusted. More specifically, the distance threshold maybe adjusted from the first threshold level, indicated by line 1526, to asecond distance threshold level, indicated by plot 1527.

With the distance threshold adjusted at time t3, between time t3 and t4,a distance determination of the object of interest from the vehicleexhaust may be determined via the ultrasonic sensor (e.g. 185). Toimprove operational use of the ultrasonic sensor, a distance detectionthreshold may be adjusted based on the indicated humidity andtemperature, as discussed above in detail with regard to step 1155 atFIG. 11, and with regard to step 1230 at FIG. 12. As such, a distancemeasurement may be conducted between time t3 and t4 via the use of theultrasonic sensor, such that an object position may be determined attime t4. Because the distance threshold was adjusted to the seconddistance threshold, indicated by line 1527, and because the object isindicated to be positioned at a distance greater than the adjusteddistance threshold, a DPF regeneration procedure may be conducted.Accordingly, at time t4, DPF regeneration is initiated, indicated byplot 1530.

As discussed above, regenerating the DPF may include adjusting engineoperating parameters to increase DPF temperature. Examples may includeoperating a heater (e.g. 75) coupled to the DPF, or by raising atemperature of engine exhaust by operating rich, or by direct injectionof fuel into exhaust gas.

Between time t4 and t5, regeneration of the DPF may be conducted. Whilenot explicitly shown, it may be understood that during the DPFregeneration procedure, one or more of the onboard camera(s) andultrasonic sensor(s) may be continued to be utilized in order toindicate whether an object has moved into an area below the adjustedthreshold distance. In such a case where an object is indicated to bebelow the adjusted threshold distance, the regeneration event may beterminated, and may in some examples be postponed.

Furthermore, between time t4 and t5, while the DPF regenerationprocedure is in progress, soot load may be monitored via, for example apressure differential across the DPF. Responsive to the pressuredifferential decreasing to a predetermined threshold pressuredifferential, the DPF regeneration procedure may end. Accordingly, attime t5 it may be understood that the DPF has been regenerated.Accordingly, the DPF regeneration procedure is terminated, indicated byplot 1530, as DPF regeneration conditions are no longer met, indicatedby plot 1505. Furthermore, object detection operations may cease, as itis no longer desired to indicate whether an object is positioned in aproximity close to the vehicle exhaust, indicated by plot 1515.

Between time t5 and t6, vehicle speed increases, as the vehicle resumestypical driving operation.

In this way, a relative humidity measurement may be determined via useof an ultrasonic sensor positioned around a motor vehicle, where theultrasonic sensor is selected from a plurality of ultrasonic sensors. Inthis way, only the ultrasonic sensor that may be likely to providerobust relative humidity measurements with desired accuracy may beutilized, which may thus increase lifetime of the plurality ofultrasonic sensors positioned around the vehicle. Furthermore, anability to selectively utilize an ultrasonic sensor for relativehumidity measurements may be advantageous under conditions where adiesel particulate filter needs regenerating, where the relativehumidity estimation may enable an adjustment of a distance thresholdbetween an object and an exhaust of the vehicle.

The technical effect is to recognize that in a vehicle with a pluralityof ultrasonic sensors, certain conditions may make the use of oneultrasonic sensor preferable to the use of the other ultrasonic sensors,when conducting a relative humidity determination. Selecting thepreferred ultrasonic sensor may be conducted by determining objects ofinterest proximal to the vehicle, via the use of one or more onboardcameras configured to detect and indicate potential object(s) ofinterest. Upon identification of an object of interest, the preferredultrasonic sensor may be selected, and a relative humidity measurementconducted. Conducting relative humidity estimations in this way mayimprove accuracy and robustness of the relative humidity determinations.By improving accuracy and robustness of relative humidity estimationsconducted via an ultrasonic sensor, vehicle operating conditions thatdepend on an accurate knowledge of relative humidity, may be improved.

The systems described herein, and with regard to FIGS. 1-2 and FIG. 8,along with the methods described herein and with regard to FIGS. 4-7,FIG. 9, and FIGS. 11-12, may enable one or more systems, and one or moremethods. In one example, a method comprises selecting one of a pluralityof sensors positioned around a motor vehicle; transmitting a pluralityof signals from the selected sensor, each at a different frequency;receiving reflected signals of the transmitted signals; determiningattenuation values only for each of the reflected signals which have thesame transit time from transmission to receipt; determining differencesbetween pairs of the attenuation values; and converting the differencesto an indication of relative humidity. In a first example of the method,the method further includes wherein the selected sensor is selectedbased on there being a stationary object within a transmission path ofthe selected sensor. A second example of the method optionally includesthe first example and further includes wherein the selected sensor isselected based on there being a target vehicle traveling within atransmission path of the selected sensor and where the target vehicle istraveling at a velocity substantially equal to the motor vehiclevelocity and also at a substantially constant distance from the motorvehicle. A third example of the method optionally includes any one ormore or each of the first and second examples, and further comprisesregenerating a particulate filter coupled to an underbody of the motorvehicle by causing burning of particulate stored in the particulatefilter resulting in hot gases exiting a rear of the motor vehicle;selecting the selected sensor based on a transmission path of theselected sensor overlapping at least a portion of the hot gases exitingthe rear of the motor vehicle; and postponing or aborting theregeneration based on there being an object within a predetermineddistance of the hot gases exiting the rear of the motor vehicle. Afourth example of the method optionally includes any one or more or eachof the first through third examples, and further comprises measuring anair temperature near where the hot gases exit the rear of the motorvehicle; determining thermal conductivity of air based, at least inpart, on the indication of relative humidity and the air temperature;and adjusting a distance threshold for the regeneration procedure, wherethe adjusting the distance threshold includes decreasing the distancethreshold as thermal conductivity decreases, and increasing the distancethreshold as thermal conductivity increases. A fifth example of themethod optionally includes any one or more or each of the first throughfourth examples and further comprises conducting the regenerationprocedure without determining whether an object is within thepredetermined distance of the hot gases exiting the rear of the motorvehicle responsive to an indication that a velocity of the vehicle isgreater than a predetermined velocity threshold. A sixth example of themethod optionally includes any one or more or each of the first throughfifth examples and further comprises comparing amplitude of thereflected signal to a reference amplitude based on distance of an objectfrom which the selected signal is reflected and environmental conditionsincluding, but not limited to, humidity or temperature to determinewhenever the sensor needs to be cleaned. A seventh example of the methodoptionally includes any one or more or each of the first through sixthexamples and further includes wherein the selecting one of a pluralityof sensors positioned around the motor vehicle is based in part onwhether any of the plurality of sensors needs to be cleaned. An eighthexample of the method optionally includes any one or more or each of thefirst through seventh examples and further includes wherein thetransmitted signals comprise sound waves, and wherein the single sensorcomprises an ultrasonic sensor. A ninth example of the method optionallyincludes any one or more or each of the first through eighth examplesand further includes wherein selecting one of a plurality of sensors inorder to provide an indication of relative humidity occurs responsive toat least one of the following: a change in ambient temperature greaterthan an ambient temperature threshold, a change in ambient pressuregreater than an ambient pressure threshold, a threshold time of engineoperation exceeding an engine operation time threshold, and a distanceof vehicle travel greater than a distance threshold.

Another example of a method comprises selecting one of a plurality ofsensors positioned around a motor vehicle based in part on one or moreimages from one or more cameras positioned around the motor vehicle;transmitting a plurality of signals from the selected sensor, each at adifferent frequency; receiving reflected signals of the transmittedsignals; determining attenuation values only for each of the reflectedsignals which have the same transit time from transmission to receipt;determining differences between pairs of the attenuation values; andconverting the differences to an indication of relative humidity. In afirst example of the method, the method further includes wherein theselected sensor is selected based on an object, identified by one of thecameras, being within a transmission path of the selected sensor. Asecond example of the method optionally includes the first example andfurther includes wherein the object is stationary. A third example ofthe method optionally includes any one or more or each of the first andsecond examples and further includes wherein the object is moving at avelocity substantially equal to the motor vehicle velocity and also at asubstantially constant distance from the motor vehicle. A fourth exampleof the method optionally includes any one or more or each of the firstthrough third examples and further comprises regenerating a particulatefilter coupled to an underbody of the motor vehicle by causing burningof particulate stored in the particulate filter resulting in hot gasesexiting a rear of the motor vehicle; selecting the selected sensor basedon a transmission path of the selected sensor overlapping at least aportion of the hot gases exiting the rear of the motor vehicle, andfurther based on the object being within a transmission path of theselected sensor as identified by one of the cameras; and postponing oraborting the regeneration based on there being an object within athreshold distance of the hot gases exiting the rear of the motorvehicle, where the threshold distance is adjusted based on a measuredthermal conductivity of air. A fifth example of the method optionallyincludes any one or more or each of the first through fourth examplesand further includes wherein thermal conductivity of air is determinedbased on the indication of relative humidity and air temperature, whereair temperature is measured near where the hot gases exit the rear ofthe motor vehicle; and wherein adjusting the threshold distance based onthe measured thermal conductivity of air includes decreasing thedistance threshold as thermal conductivity decreases, and increasing thedistance threshold as thermal conductivity increases. A sixth example ofthe method optionally includes any one or more or each of the firstthrough fifth examples and further comprises conducting the regenerationprocedure responsive to the object being positioned at a greaterdistance than the threshold distance; monitoring the object and an areaproximate the rear of the vehicle via the one or more cameras during theregeneration procedure; and terminating the regeneration procedure ifthe object or other object is identified as being closer than thethreshold distance during the regeneration procedure.

A system for a vehicle comprises one or more ultrasonic sensorspositioned at various points on the vehicle; an outside air temperaturesensor; and a controller storing instructions in non-transitory memory,that when executed, cause the controller to: select one of theultrasonic sensors positioned at various points on the vehicle; measureoutside air temperature; command the ultrasonic sensor to transmit andreceive a plurality of ultrasonic signals from a single ultrasonicsensor; indicate signals that have the same transit time fromtransmission to receipt; determine attenuation values for those signalsthat have the same transit time from transmission to receipt; determinedifferences between pairs of attenuation values; and convert thedifferences to an indication of relative humidity via the use of atransfer function. In a first example, the system further comprises oneor more cameras positioned at various points on the vehicle andconfigured to obtain images proximal to the vehicle; and wherein thecontroller further stores instructions in non-transitory memory, thatwhen executed, cause the controller to: identify objects that arestationary with respect to the vehicle; and select the ultrasonic sensorresponsive to an indication that the object is within a transmissionpath of the selected sensor. A second example of the system optionallyincludes the first example and further comprises a diesel particulatefilter coupled to an underbody of the vehicle, where the dieselparticulate filter is regenerated by burning of particulate stored inthe particulate filter, resulting in hot gases exiting a rear of thevehicle; and wherein the controller further stores instructions innon-transitory memory, that when executed, cause the controller to:select the ultrasonic sensor responsive to an indication that thetransmission path of the ultrasonic sensor overlaps at least a portionof hot gases exiting a rear of the vehicle; determine a thermalconductivity of air, the thermal conductivity of air determined as afunction of the indicated relative humidity and measured airtemperature; adjust a threshold distance an object or objects can bepositioned away from the gases exiting the rear of the vehicle, whereregeneration of the particulate filter is conducted only responsive toan indication that the object or objects are positioned at a greaterdistance than the adjusted threshold distance; and wherein adjusting thethreshold distance is based on the measured thermal conductivity of airand includes decreasing the threshold distance as thermal conductivitydecreases, and increasing the threshold distance as thermal conductivityincreases.

Note that the example control and estimation routines included hereincan be used with various engine and/or vehicle system configurations.The control methods and routines disclosed herein may be stored asexecutable instructions in non-transitory memory and may be carried outby the control system including the controller in combination with thevarious sensors, actuators, and other engine hardware. The specificroutines described herein may represent one or more of any number ofprocessing strategies such as event-driven, interrupt-driven,multi-tasking, multi-threading, and the like. As such, various actions,operations, and/or functions illustrated may be performed in thesequence illustrated, in parallel, or in some cases omitted. Likewise,the order of processing is not necessarily required to achieve thefeatures and advantages of the example embodiments described herein, butis provided for ease of illustration and description. One or more of theillustrated actions, operations and/or functions may be repeatedlyperformed depending on the particular strategy being used. Further, thedescribed actions, operations and/or functions may graphically representcode to be programmed into non-transitory memory of the computerreadable storage medium in the engine control system, where thedescribed actions are carried out by executing the instructions in asystem including the various engine hardware components in combinationwith the electronic controller.

It will be appreciated that the configurations and routines disclosedherein are exemplary in nature, and that these specific embodiments arenot to be considered in a limiting sense, because numerous variationsare possible. For example, the above technology can be applied to V-6,I-4, I-6, V-12, opposed 4, and other engine types. The subject matter ofthe present disclosure includes all novel and non-obvious combinationsand sub-combinations of the various systems and configurations, andother features, functions, and/or properties disclosed herein.

The following claims particularly point out certain combinations andsub-combinations regarded as novel and non-obvious. These claims mayrefer to “an” element or “a first” element or the equivalent thereof.Such claims should be understood to include incorporation of one or moresuch elements, neither requiring nor excluding two or more suchelements. Other combinations and sub-combinations of the disclosedfeatures, functions, elements, and/or properties may be claimed throughamendment of the present claims or through presentation of new claims inthis or a related application. Such claims, whether broader, narrower,equal, or different in scope to the original claims, also are regardedas included within the subject matter of the present disclosure.

The invention claimed is:
 1. A method, comprising: selecting one of aplurality of sensors positioned around a motor vehicle based on therebeing a stationary object with respect to the motor vehicle within atransmission path of the selected sensor; transmitting a plurality ofsignals from the selected sensor, each at a different frequency;receiving reflected signals of the transmitted signals; determiningattenuation values only for each of the reflected signals which have asame transit time from transmission to receipt; determining differencesbetween pairs of the attenuation values; and converting the differencesto an indication of relative humidity.
 2. The method of claim 1, whereinthe selected sensor is selected based on there being a target vehicletraveling within a transmission path of the selected sensor and wherethe target vehicle is traveling at a velocity substantially equal to avelocity of the motor vehicle and also at a substantially constantdistance from the motor vehicle.
 3. The method of claim 1, furthercomprising: regenerating a particulate filter coupled to an underbody ofthe motor vehicle by causing burning of particulates stored in theparticulate filter resulting in gases exiting a rear of the motorvehicle; selecting the selected sensor based on the transmission path ofthe selected sensor overlapping at least a portion of the gases exitingthe rear of the motor vehicle; and postponing or aborting theregeneration based on there being an object within a predetermineddistance of the gases exiting the rear of the motor vehicle.
 4. Themethod of claim 3, further comprising: measuring an air temperature nearwhere the gases exit the rear of the motor vehicle; determining thermalconductivity of air based, at least in part, on the indication ofrelative humidity and the air temperature; and adjusting a distancethreshold for the regeneration procedure, where the adjusting thedistance threshold includes decreasing the distance threshold as thermalconductivity decreases, and increasing the distance threshold as thermalconductivity increases.
 5. The method of claim 3, further comprising:conducting the regeneration procedure without determining whether theobject is within the predetermined distance of the gases exiting therear of the motor vehicle responsive to an indication that a velocity ofthe motor vehicle is greater than a predetermined velocity threshold. 6.The method of claim 1, further comprising: comparing amplitude of thereflected signals to a reference amplitude based on distance of thestationary object from which the selected signal is reflected andenvironmental conditions including, but not limited to, humidity ortemperature to determine whenever the selected sensor needs to becleaned.
 7. The method of claim 6, wherein the selecting one of theplurality of sensors positioned around the motor vehicle is based inpart on whether any of the plurality of sensors needs to be cleaned. 8.The method of claim 1, wherein the transmitted signals comprise soundwaves, and wherein the selected sensor comprises an ultrasonic sensor.9. The method of claim 1, wherein selecting one of the plurality ofsensors in order to provide the indication of relative humidity occursresponsive to at least one of the following: a change in ambienttemperature greater than an ambient temperature threshold, a change inambient pressure greater than an ambient pressure threshold, a thresholdtime of engine operation exceeding an engine operation time threshold,and a distance of vehicle travel greater than a distance threshold. 10.A method, comprising: selecting one of a plurality of sensors positionedaround a motor vehicle based in part on one or more images from one ormore cameras positioned around the motor vehicle; transmitting aplurality of signals from the selected sensor, each at a differentfrequency; receiving reflected signals of the transmitted signals;determining attenuation values only for each of the reflected signalswhich have a same transit time from transmission to receipt; determiningdifferences between pairs of the attenuation values; and converting thedifferences to an indication of relative humidity.
 11. The method ofclaim 10, wherein the selected sensor is selected based on an object,identified by one of the cameras, being within a transmission path ofthe selected sensor.
 12. The method of claim 11, wherein the object isstationary.
 13. The method of claim 11, wherein the object is moving ata velocity substantially equal to a velocity of the motor vehicle andalso at a substantially constant distance from the motor vehicle. 14.The method of claim 11, further comprising: regenerating a particulatefilter coupled to an underbody of the motor vehicle by causing burningof particulates stored in the particulate filter resulting in gasesexiting a rear of the motor vehicle; selecting the selected sensor basedon the transmission path of the selected sensor overlapping at least aportion of the gases exiting the rear of the motor vehicle, and furtherbased on the object being within the transmission path of the selectedsensor as identified by one of the cameras; and postponing or abortingthe regeneration based on there being an object within a thresholddistance of the gases exiting the rear of the motor vehicle, where thethreshold distance is adjusted based on a measured thermal conductivityof air.
 15. The method of claim 14, wherein the thermal conductivity ofair is determined based on the indication of relative humidity and airtemperature, where air temperature is measured near where the gases exitthe rear of the motor vehicle; and wherein adjusting the thresholddistance based on the measured thermal conductivity of air includesdecreasing the threshold distance as thermal conductivity decreases, andincreasing the threshold distance as thermal conductivity increases. 16.The method of claim 14, further comprising: conducting the regenerationresponsive to the object being positioned at a greater distance than thethreshold distance; monitoring the object and an area proximate the rearof the vehicle via the one or more cameras during the regeneration; andterminating the regeneration if the object or other object is identifiedas being closer than the threshold distance during the regeneration. 17.A system for a vehicle, comprising: one or more ultrasonic sensorspositioned at various points on the vehicle; an outside air temperaturesensor; and a controller storing instructions in non-transitory memory,that when executed, cause the controller to: select one of theultrasonic sensors positioned at various points on the vehicle based onan object being within a transmission path of the selected ultrasonicsensor; measure outside air temperature; command the selected ultrasonicsensor to transmit and receive a plurality of ultrasonic signals fromthe selected ultrasonic sensor; indicate signals that have a sametransit time from transmission to receipt; determine attenuation valuesfor those signals that have the same transit time from transmission toreceipt; determine differences between pairs of attenuation values; andconvert the differences to an indication of relative humidity via use ofa transfer function.
 18. The system of claim 17, further comprising: oneor more cameras positioned at various points on the vehicle andconfigured to obtain images proximal to the vehicle; and wherein thecontroller further stores instructions in non-transitory memory, thatwhen executed, cause the controller to: identify the object being withinthe transmission path of the selected ultrasonic sensor via the one ormore cameras, where the object is further determined to be stationarywith respect to the vehicle.
 19. The system of claim 17, furthercomprising: a diesel particulate filter coupled to an underbody of thevehicle, where the diesel particulate filter is regenerated by burningof particulates stored in the diesel particulate filter, resulting ingases exiting a rear of the vehicle; and wherein the controller furtherstores instructions in non-transitory memory, that when executed, causethe controller to: select the selected ultrasonic sensor furtherresponsive to an indication that the transmission path of the selectedultrasonic sensor overlaps at least a portion of the gases exiting therear of the vehicle; determine a thermal conductivity of air, thethermal conductivity of air determined as a function of the indicatedrelative humidity and measured air temperature; adjust a thresholddistance the object can be positioned away from the gases exiting therear of the vehicle, where regeneration of the diesel particulate filteris conducted only responsive to an indication that the object ispositioned at a greater distance than the adjusted threshold distance;and wherein adjusting the threshold distance is based on the determinedthermal conductivity of air and includes decreasing the thresholddistance as thermal conductivity decreases, and increasing the thresholddistance as thermal conductivity increases.